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Primary Maths · Year 6Chapter 6 · Percentages
Year 6 · Chapter 6

Year 6 Percentages: worked examples and questions with answers

By the end of this chapter you will be able to

  • Change between fractions, decimals and percentages, and know the common equivalences by heart
  • Find 10%, 1%, 50%, 25% and 75% of an amount, using the building blocks
  • Find a percentage of a measure, such as 15% of 360, and of an amount of money
  • Write one amount as a percentage of a whole, and find the whole from a percentage
  • Compare percentages from different totals, and savings in pounds, to say which is better
  • Estimate and check percentage answers, and explain your reasoning about them

You should already know

  • Fractions, decimals and place value to three decimal places (Year 6, Chapters 4 and 5)
  • Equivalent fractions and simplifying (Year 6, Chapter 4)
  • Multiplying and dividing decimals by 10, 100 and 1000 (Year 6, Chapter 5)
  • Per cent as out of 100, and the fractions and decimals of 1/2 and 1/4 (Year 5, Chapter 7)

Where this leads

  • Ratio and proportion, where percentages are one way to compare amounts (Year 6, Chapter 7)
  • Measures and conversions, with percentages of lengths and masses (Year 6, Chapter 9)
  • Statistics: pie charts and percentages of a whole (Year 6, Chapter 12)

National Curriculum for England, Key Stage 2 mathematics, Year 6. Content: Recall and use equivalences between simple fractions, decimals and percentages, including in different contexts, Solve problems involving the calculation of percentages (of measures, such as 15% of 360), Solve problems involving the use of percentages for comparison.

Exercise P  Do you remember?

Non-calculator
1
FWhat is 3/4 as a decimal?
2
FWork out 0.6 × 4.
3
FWrite 25/100 in its simplest form.
4
FWork out 360 ÷ 10.
5
FRound 6.45 to one decimal place.
6.1

Per cent, fractions and decimals

Year 6
Recall and use equivalences between simple fractions, decimals and percentages, including in different contexts
Video lesson: Per cent, fractions and decimalsComing soon

A percentage is a fraction with 100 as the bottom number. The word comes from per cent, which means out of 100. If 35 squares of a 100 square are shaded, then 35 out of 100 are shaded: that is 35%.

A percentage, a decimal and a fraction can all name the same amount. 35% is 35/100, which is 0.35. Once you know these equivalences, you can change between the three forms quickly.

35 out of 100 = 35%
The 100 grid: 35 of the 100 squares are shaded.
0%025%1/450%1/275%3/4100%1
Quarters of the way along a number line, written three ways.
FractionDecimalPercentage
1/20.550%
1/40.2525%
3/40.7575%
1/50.220%
2/50.440%
3/50.660%
4/50.880%
1/100.110%
1/200.055%
1/250.044%
1/80.12512.5%
3/80.37537.5%

Learn these pairs. Each one is worth knowing well.

Key ideas

  • Per cent means out of 100. The sign % shows it.
  • To change a percentage to a decimal, divide by 100 (move the point two places left): 35% = 0.35.
  • To change a decimal to a percentage, multiply by 100 (move the point two places right): 0.7 = 70%.
  • To change a fraction to a percentage, make the bottom number 100 or divide, then multiply by 100: 3/8 = 37.5%.
Worked example 6.1.1
Write 0.35 as a percentage.

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Multiply the decimal by 100. The answer is the number of per cent.

  1. Write the decimal. Read the decimal carefully, with its point.
    0.35
  2. Multiply by 100: move the decimal point two places to the right. Multiplying by 100 gives the number of hundredths, which is per cent.
    0.35 × 100 = 35
  3. Write the answer as a percentage. So the decimal is this many out of 100.
    35

Check. 35% ÷ 100 = 0.35. ✓

Watch out. Do not forget the step. 0.7 is 70%, not 7%.

Worked example 6.1.2
Write 3/8 as a percentage.

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Change the fraction to a decimal, then multiply it by 100.

  1. Divide the top number by the bottom number. A fraction bar means divide.
    3 ÷ 8 = 0.375
  2. Multiply the decimal by 100. That turns the decimal into per cent.
    0.375 × 100 = 37.5
  3. Write the answer.
    37.5

Check. 37.5% ÷ 100 = 0.375, which is the same as the fraction we started with. ✓

Watch out. Multiply by 100 at the end, not at the start.

Worked example 6.1.3
Write 60% as a fraction in its simplest form.

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Write 60% out of 100, then simplify the fraction.

  1. Write the percentage as a fraction out of 100. Per cent means out of 100.
    60% = 60/100
  2. Find the highest common factor (HCF) of the top and the bottom. It is the biggest number that divides into both.
    HCF of 60 and 100 is 20
  3. Divide the top and the bottom by the HCF. This makes the fraction as simple as possible.
    60 ÷ 20 = 3, and 100 ÷ 20 = 5
  4. Write the answer.
    3/5

Check. 3/5 as a percentage is 60%. ✓

Watch out. Simplify by dividing the top and the bottom by the same number, not by taking away.

Watch out

0.4 is 40%, not 4%. Many pupils move the point the wrong way. 4% is 0.04, which is a tenth of 0.4.

Exam tip

Grown-up tip. Ask: “Out of 100, how many?” Most questions become easy once the bottom number is 100.

Exercise 6A  Fractions, decimals and percentages

Non-calculator
1
FWrite each percentage as a fraction in its simplest form.
(a)50% =
(b)20% =
(c)75% =
(d)40% =
2
FWrite each percentage as a decimal.
(a)60% =
(b)5% =
(c)35% =
(d)8% =
3
FWrite each decimal as a percentage (give the number of %).
(a)0.7 =
(b)0.45 =
(c)0.03 =
(d)0.125 =
4
FWrite each fraction as a percentage (give the number of %).
(a)3/5 =
(b)7/20 =
(c)9/25 =
(d)1/8 =
5
PSA pizza is cut into 8 equal slices. Ali eats 3 slices. What percentage (%) of the pizza has he eaten?
6
FTick the three numbers that are equal to 0.4:   4/10   40%   4%   0.04   2/5
7
FPut these in order, smallest first:   0.3   35%   1/4   0.22
8
RTom says that 1/8 is 18%. Is he right? Explain your answer.
9
FWrite each fraction as a percentage.
(a)1/10 =
(b)1/20 =
(c)1/25 =
(d)3/50 =
10
FWrite each decimal as a fraction in its simplest form.
(a)0.8 =
(b)0.04 =
(c)0.75 =
11
PSMia reads 0.125 of a 240-page book on Monday. What percentage (%) of the book has she read?
12
RRavi says that 3/8, 0.375 and 37% are all the same. Is he right? Explain your answer.
6.2

Percentages in real life

Year 6
Recall and use equivalences between simple fractions, decimals and percentages, including in different contexts
Video lesson: Percentages in real lifeComing soon

Percentages are used everywhere: on phone batteries, in test results, in sales and in surveys. In each of these, the question is always the same: what part of the whole is it?

Start with a fraction (the part out of the whole). Then make the bottom number 100, or divide to find a decimal and multiply by 100. The answer is the percentage. Look at the units too: 90 minutes is 90 out of 120 minutes in a 2-hour film, not 90 out of 2.

75%25%100% of the jug
A jug that is three quarters full.

Key ideas

  • A percentage is always a part out of 100.
  • To write a part as a percentage of a whole: part ÷ whole, then × 100.
  • Make the units the same before you divide. 50 cm is 0.5 m, and 15 minutes is 15 out of 60 minutes.
  • Some common results to know: 1/2 = 50%, 1/4 = 25%, 3/4 = 75%, 1/5 = 20%, 1/10 = 10%.
Worked example 6.2.1
Sam gets 18 out of 25 in a spelling test. What percentage (%) did he get?

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Make the bottom number 100 by multiplying by 4.

  1. Make the bottom number 100. 25 × 4 = 100, so multiply the top and the bottom by 4.
    18/25 = 72/100
  2. Read the top number as per cent. Out of 100 means per cent.
    72/100 = 72%
  3. Write the answer.
    72

Check. 72% ÷ 100 = 0.72, which is the same as the fraction we started with. ✓

Watch out. Multiply by 100 at the end, not at the start.

Worked example 6.2.2
What percentage (%) of an hour is 15 minutes?

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Change the fraction to a decimal, then multiply it by 100.

  1. Divide the top number by the bottom number. A fraction bar means divide.
    15 ÷ 60 = 0.25
  2. Multiply the decimal by 100. That turns the decimal into per cent.
    0.25 × 100 = 25
  3. Write the answer.
    25

Check. 25% ÷ 100 = 0.25, which is the same as the fraction we started with. ✓

Watch out. Multiply by 100 at the end, not at the start.

Worked example 6.2.3
Ella spent £15 of her £20. What percentage (%) did she spend?

Key words. Per cent means out of 100. The sign % means per cent, so 35% means 35 out of 100. It can be written as the fraction 35/100 or the decimal 0.35.

Method. Make the bottom number 100 by multiplying by 5.

  1. Make the bottom number 100. 20 × 5 = 100, so multiply the top and the bottom by 5.
    15/20 = 75/100
  2. Read the top number as per cent. Out of 100 means per cent.
    75/100 = 75%
  3. Write the answer.
    75

Check. 75% ÷ 100 = 0.75, which is the same as the fraction we started with. ✓

Watch out. Multiply by 100 at the end, not at the start.

Watch out

Check the bottom number first. 15 minutes out of 60 minutes is the right fraction. 15 out of 60 is not the same as 15 out of 15.

Exam tip

Grown-up tip. Ask: “What is the whole?” Many children can find the part, but they put it on the wrong side.

Exercise 6B  Percentages in real-life contexts

Non-calculator
1
FA jug is 3/4 full. What percentage (%) of the jug is full?
2
FA class has 30 pupils. 6 of them walk to school. What percentage (%) of the class walk to school?
3
FThe battery on Ravi’s phone shows 0.6. What percentage (%) of the battery is charged?
4
FA film lasts 2 hours. Sam has watched 90 minutes of it. What percentage (%) of the film has he watched?
5
FA rope is 2 m long. Sam cuts off 50 cm. What percentage (%) of the rope has he cut off?
6
FLena collected 35 stickers. 7 of them are gold. What percentage (%) of her stickers are gold?
7
FAli answered 17 out of 20 questions correctly. What percentage (%) did he get right?
8
PSA school has 400 pupils. 120 of them have school dinners. What percentage (%) of the pupils have school dinners?
9
PSIn a survey, 0.45 of the pupils said they like maths. What percentage (%) of the pupils like maths?
10
PSA bag holds 50 marbles. 12 of them are blue. What percentage (%) of the marbles are blue?
11
PSMina has read 0.375 of her library book. What percentage (%) of the book has she read?
12
PSA race is 5 km long. Jo has run 1.25 km. What percentage (%) of the race has she run?
13
RJack says, “3 out of 4 is the same as 0.75 and as 75%.” Is he right? Explain your answer.
14
RBen says that 15 minutes is 15% of an hour. Is he right? Explain your answer.
6.3

Building blocks: 10%, 1%, 50%, 25% and 75%

Year 6
Solve problems involving the calculation of percentages (of measures, such as 15% of 360)
Video lesson: Building blocks: 10%, 1%, 50%, 25% and 75%Coming soon

Some percentages are easy to find in your head. They are the building blocks for harder ones like 15% or 35%.

Once you know 10% and 1%, you can build many other percentages from them. For example, 5% is half of 10%.

10 out of 100 = 10%
Ten squares are 10% of the grid. Dividing the whole by 10 gives 10%.

Key ideas

  • 10% of a number: divide by 10.
  • 1% of a number: divide by 100.
  • 50% = half, 25% = a quarter, 75% = three quarters.
  • Use the building blocks to find other percentages: 20% is 2 × 10%, and 5% is half of 10%.
Worked example 6.3.1
Find 10% of 260.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. 10% is one tenth, so divide by 10.

  1. Write 10% as a fraction. 10 out of 100 is one tenth.
    10% = 10/100 = 1/10
  2. Divide the amount by 10. One tenth of the amount is found by dividing by 10.
    260 ÷ 10 = 26
  3. Write the answer. The answer is smaller than the amount.
    26

Check. 26 × 10 = 260. ✓

Watch out. 10% of 50 is 5, not 40. Dividing by 10 is not the same as taking 10 away.

Worked example 6.3.2
Find 1% of 360.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find 1% by dividing the amount by 100.

  1. Write the percentage as a fraction out of 100. Per cent means out of 100.
    1% = 1/100
  2. Find 1% of 360. Divide by 100, because 1% is one hundredth.
    360 ÷ 100 = 3.6
  3. Write the answer.
    3.6

Check. 3.6 is less than 360, because 1% is less than 100%. ✓

Watch out. Dividing by 100 gives 1%. Do not multiply by 1 before you divide.

Worked example 6.3.3
Find 75% of 200.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find one quarter first, then take three of those quarters.

  1. Write 75% as a fraction. 75 out of 100 is 3 quarters, because 25% is 1/4.
    75% = 3/4
  2. Find one quarter: divide by 4. One quarter is 25%.
    200 ÷ 4 = 50
  3. Multiply by 3. Three quarters is three lots of one quarter.
    50 × 3 = 150
  4. Write the answer.
    150

Check. 150 is less than 200, because 75% is less than 100%. ✓

Watch out. Do not find 25% and stop. The question asks for 75%, so take three quarters.

Watch out

1% of 360 is 3.6, not 36. Dividing by 100 makes the number 100 times smaller, so the answer is a decimal.

Exam tip

Grown-up tip. Practise the building blocks aloud: “10% of 80 is 8, so 20% is 16.” Quick recall helps with the next section.

Exercise 6C  Percentages of amounts: the building blocks

Non-calculator
1
FFind 10% of each amount.
(a)10% of 50 =
(b)10% of 230 =
(c)10% of 780 =
(d)10% of 40 =
2
FFind 1% of each amount.
(a)1% of 500 =
(b)1% of 80 =
(c)1% of 2400 =
(d)1% of 7 =
3
FFind 50% of each amount.
(a)50% of 64 =
(b)50% of 37 =
(c)50% of 9 =
4
FFind 25% of each amount.
(a)25% of 60 =
(b)25% of 90 =
(c)25% of 36 =
5
FFind 75% of each amount.
(a)75% of 200 =
(b)75% of 40 =
(c)75% of 12 =
6
FQuick-fire! Work out each percentage.
(a)10% of 90 =
(b)1% of 450 =
(c)50% of 90 =
(d)25% of 36 =
(e)75% of 16 =
(f)10% of 4.5 =
7
PSA bag holds 250 g of sweets. Sam eats 10% of the sweets. How many grams (g) does he eat?
8
PSA school raises £640. 25% of the money goes to charity. How much (£) goes to charity?
9
PSA pizza costs £12. Mia gets 50% off the price, so she pays half. How much (£) does she pay?
10
PSJack has 80 stickers. He gives away 25% of them. How many stickers does he have left?
11
PSA town has 3600 homes. 1% of the homes have solar panels. How many homes have solar panels?
12
PSA sports club has 120 members. 75% of them are under 12. How many members are under 12?
13
RSam says that 10% of 500 is the same as 1% of 5000. Is he right? Explain your answer.
14
RElla says that 50% of 60 is the same as 25% of 120. Is she right? Explain your answer.
6.4

Percentages of measures

Year 6
Solve problems involving the calculation of percentages (of measures, such as 15% of 360)
Video lesson: Percentages of measuresComing soon

A percentage of a measure is a part of an amount, such as a length, a mass, a volume or a sum of money. Two methods always work.

  1. Build it from 10%. Find 10% (divide by 10), then add the parts you need: 5% is half of 10%, and 1% is a tenth of 10%.
  2. Use 1% first. Divide the amount by 100 to find 1%, then multiply by the percentage.

For 15% of 360: 10% is 36, and 5% is half of 36, which is 18. So 15% is 36 + 18 = 54.

10%5%85%100% of 360
The whole bar is 360. Its 10% part is 36, and its 5% part is 18.

Key ideas

  • A percentage of a measure is the same as the percentage times the amount, divided by 100.
  • 10% is one tenth. 5% is half of 10%. 1% is one hundredth.
  • Make the units the same before you calculate: 1 kg = 1000 g, 1 m = 100 cm, 1 litre = 1000 ml.
  • Check that your answer is sensible: 15% of 360 must be less than 360.
Worked example 6.4.1
Find 15% of 360.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find 10% first, then add the 5% and 1% parts that make up 15%.

  1. Split 15% into 10%, 5% and 1% parts. Ten, five and one make the parts we can find easily.
    15% = 1 lot of 10% + 5%
  2. Find 10% of 360, then 1 lot. 10% is one tenth, so divide by 10.
    10% of 360 = 36; 1 × 36 = 36
  3. Find 5%. Half of 10% is 5%, so halve the 10% answer.
    5% of 360 = 36 ÷ 2 = 18
  4. Add the parts. Add the answers for each part to find the whole percentage.
    36 + 18 = 54

Check. Fraction check: 15/100 × 360 = 54. ✓

Watch out. Check the parts: 10% is a tenth, so divide by 10. 1% is divide by 100.

Worked example 6.4.2
Find 35% of 40 kg. Give the answer in kilograms (kg).

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find 1% first by dividing by 100, then multiply by 35.

  1. Write the percentage as a fraction out of 100. Per cent means out of 100.
    35% = 35/100
  2. Find 1% of 40. Divide by 100, because 1% is one hundredth.
    40 ÷ 100 = 0.4
  3. Multiply by 35. 35% is 35 lots of 1%.
    0.4 × 35 = 14
  4. Write the answer.
    14

Check. 14 is less than 40, because 35% is less than 100%. ✓

Watch out. Dividing by 100 gives 1%. Do not multiply by 35 before you divide.

Worked example 6.4.3
Find 12% of £4.50.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find 1% first by dividing by 100, then multiply by 12.

  1. Write the percentage as a fraction out of 100. Per cent means out of 100.
    12% = 12/100
  2. Find 1% of 4.5. Divide by 100, because 1% is one hundredth.
    4.5 ÷ 100 = 0.045
  3. Multiply by 12. 12% is 12 lots of 1%.
    0.045 × 12 = 0.54
  4. Write the answer.
    0.54

Check. 0.54 is less than 4.5, because 12% is less than 100%. ✓

Watch out. Dividing by 100 gives 1%. Do not multiply by 12 before you divide.

Watch out

Take care with the decimal point. 1% of £4.50 is 4.5 ÷ 100 = 0.045, and 12 lots of that make 0.54. Your answer must be in pounds and pence.

Exam tip

Exam tip. If you are not sure which method to use, find 10% and 1% first. Those two are always quick.

Exercise 6D  Finding percentages of measures

Non-calculator
1
FFind each percentage.
(a)15% of 80 =
(b)15% of 200 =
(c)35% of 60 =
(d)5% of 260 =
2
FFind each percentage.
(a)40% of 90 =
(b)60% of 45 =
(c)8% of 150 =
(d)17% of 300 =
3
FQuick-fire! Work out each percentage.
(a)2% of 50 =
(b)9% of 200 =
(c)12% of 50 =
(d)30% of 70 =
(e)65% of 20 =
(f)90% of 30 =
4
PSA ribbon is 240 cm long. Ella uses 35% of it. How many centimetres (cm) does she use?
5
PSA bag of rice holds 2 kg. Lee uses 15% of the rice. How many grams (g) does he use? (1 kg = 1000 g.)
6
PSA water tank holds 3.5 litres when full. It is filled to 40% of its capacity. How many litres (l) of water are in it?
7
PSTara walks 15% of a 6.4 km journey. How many kilometres (km) does she walk?
8
PSMia saves 35% of her £80 pocket money. How much (£) does she save?
9
PSA school day lasts 300 minutes. 20% of the day is spent in assemblies. How many minutes (min) is that?
10
PSFind 6% of £2.50. Give your answer in pounds (£).
11
RAli says that 15% of 200 is 30. Bea says that 20% of 150 is 30. Who is right? Explain your answer.
12
RBen says that 25% of 80 is more than 80% of 25. Is he right? Explain your answer.
6.5

Using percentages to compare

Year 6
Solve problems involving the calculation of percentages and the use of percentages for comparison
Video lesson: Using percentages to compareComing soon

Percentages let us compare things that have different totals. A class of 20 and a class of 40 cannot be compared by counting, but their percentages can. The rule is simple: change each amount to a percentage first, then compare.

For money, the saving is worked out in pounds, so compare the pounds saved. Do not compare the percentages of different prices.

Class 6A40%Class 6B37.5%
Football: 40% of class 6A chose it, and 37.5% of class 6B chose it.

Key ideas

  • To compare two amounts out of different totals, change both to percentages first.
  • A percentage is out of 100, so bigger percentages are bigger shares.
  • For a sale, find the saving in pounds with the percentage, then compare the savings.
  • If two answers are the same, say so: “They are both £6.”
Worked example 6.5.1
Which is the better result: 18 out of 25 or 15 out of 20?

Key words. The part is the number we are interested in. The whole is the total. To write a part as a percentage of the whole, divide the part by the whole and then multiply by 100.

Method. Change each one to a percentage out of 100, then compare.

  1. Change 18 out of 25 to a percentage. 18/25 = 0.72, and 0.72 × 100 = 72.
    18/25 = 72%
  2. Change 15 out of 20 to a percentage. 15/20 = 0.75, and 0.75 × 100 = 75.
    15/20 = 75%
  3. Compare the two percentages. Both are out of 100, so the bigger number is the bigger share.
    72% < 75%
  4. Write the answer.
    15 out of 20 is the bigger share (75% against 72%).

Check. 72% is less than 75%, so the second result is better. ✓

Watch out. Compare percentages, not the numbers on top. 18 is more than 15, but 15 out of 20 is the bigger share.

Worked example 6.5.2
Shop A takes 20% off a £45 jacket. Shop B takes £8 off a £40 jacket. Which shop saves more money?

Key words. The part is the number we are interested in. The whole is the total. To write a part as a percentage of the whole, divide the part by the whole and then multiply by 100.

Method. Find the saving in pounds for each shop, then compare the savings.

  1. Find the saving at Shop A: 20% of £45. 1% of £45 is £0.45, so 20% is 20 lots of that.
    20% of 45 = 9
  2. Find the saving at Shop B. Shop B takes £8 off the price.
    Saving = 8
  3. Compare the savings. The bigger saving is the better offer.
    9 > 8
  4. Write the answer.
    Shop A saves more: £9 against £8.

Check. Shop A: £45 − £9 = £36. Shop B: £40 − £8 = £32. Shop A saves more, although the two jackets have different prices. ✓

Watch out. Find the saving in pounds, then compare. Do not compare 20% with £8.

Worked example 6.5.3
In class 6A, 12 of 30 pupils chose football. In class 6B, 15 of 40 pupils chose football. Which class has the bigger percentage?

Key words. The part is the number we are interested in. The whole is the total. To write a part as a percentage of the whole, divide the part by the whole and then multiply by 100.

Method. Change both results to percentages of the class, then compare.

  1. Change class 6A to a percentage. 12 out of 30 pupils.
    12/30 = 40%
  2. Change class 6B to a percentage. 15 out of 40 pupils. 15 ÷ 40 = 0.375.
    15/40 = 0.375 = 37.5%
  3. Compare. 40 is bigger than 37.5.
    40% > 37.5%
  4. Write the answer.
    Class 6A (40% against 37.5%).

Check. Class 6A has the bigger percentage, even though 6B has more pupils who chose football. ✓

Watch out. More pupils does not always mean a bigger percentage.

Watch out

Do not compare the top numbers. 15 is less than 18, but 15 out of 20 (75%) is a bigger share than 18 out of 25 (72%).

Exam tip

Exam tip. When a question asks which is better, write both percentages and then say which is bigger in words.

Exercise 6E  Comparing with percentages

Non-calculator
1
FWhich is greater, 3/5 or 58%?
2
FWhich is more: 3/4 of a cake or 70% of a cake?
3
PSAva scored 18 out of 25 in a test. Ben scored 33 out of 40. Who did better, as a percentage?
4
PSWhich is more: 20% of 250 or 35% of 120?
5
PSShop X takes 25% off a £60 coat. Shop Y takes £14 off a £70 coat. Which shop gives the bigger saving?
6
PSShop P takes 30% off a £20 jumper. Shop Q takes a quarter off a £24 jumper. Which saving is bigger?
7
PSIn Year 4, 24 of 60 pupils like cats. In Year 5, 27 of 75 pupils like cats. Which year has the greater percentage of pupils who like cats?
8
PSElla has 150 stamps, and 40% are from Europe. Jack has 120 stamps, and 45% are from Europe. Who has more European stamps?
9
RMia says that 30% of 200 is bigger than 25% of 250, because 30 is bigger than 25. Is she right? Explain your answer.
10
RIs 7/8 greater than 85%? Explain your answer.
11
PSIn a class of 40 pupils, 12 are left-handed. In a class of 25 pupils, 8 are left-handed. Which class has the greater percentage of left-handed pupils?
6.6

Estimating, checking and solving percentage problems

Year 6
Solve problems involving the calculation of percentages (of measures) and the use of percentages for comparison
Video lesson: Estimating, checking and solving percentage problemsComing soon

Good mathematicians check their answers. Before you calculate, estimate: change the numbers to easy ones, such as 50% for 48% or 200 for 199. Your estimate tells you roughly what size the answer should be.

Some questions give you a percentage of the amount you want to find. For example, if 30% of a number is 45, then 1% is 45 ÷ 30 = 1.5, and the whole (100%) is 1.5 × 100 = 150. Look carefully at which amount is the whole.

45?the whole amount
30% of the whole is 45. The rest of the bar is the 70% we do not know yet.

Key ideas

  • Estimate first by changing the numbers to easy ones: 48% is about 50%.
  • To find the whole from a percentage: find 1%, then multiply by 100.
  • Solve a long problem in steps. Write down each answer before you use it.
  • Check the answer: does it make sense, and is it the size you estimated?
Worked example 6.6.1
Estimate 48% of 199.

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Replace the numbers with easier ones, work out the estimate, then check it.

  1. Use easier numbers. 48% is about 50%, and 199 is about 200.
    48% ≈ 50%, 199 ≈ 200
  2. Work out 50% of 200. 50% of 200 is easy to find.
    50% of 200 = 100
  3. Write the estimate. The answer is about this size.
    100
  4. Check with the exact value. The exact answer is 95.52, which is close to the estimate.
    48% of 199 = 95.52

Check. The estimate 100 and the exact answer 95.52 are close. ✓

Watch out. An estimate tells you if an answer is sensible. It does not replace the exact answer.

Worked example 6.6.2
A bike costs £240. The sale takes 15% off. How much does the bike cost in the sale (£)?

Key words. Of means multiply. So 15% of 360 means 15% × 360. To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply.

Method. Find the discount first, then take it from the price to find the sale price.

  1. Find 15% of the total. This is the part that is given away.
    15% of 240 = 36
  2. Take that part away from the total. What is left is the rest.
    240 − 36 = 204
  3. Write the answer.
    204

Check. 36 + 204 = 240. ✓

Watch out. Two steps: first find the part, then take it away. Do not stop after the first step.

Worked example 6.6.3
30% of a number is 45. What is the number?

Key words. The part is the number we are interested in. The whole is the total. To write a part as a percentage of the whole, divide the part by the whole and then multiply by 100.

Method. Find 1% of the whole first, then multiply by 100 to find the whole.

  1. Write what we know. 30% of the whole amount is 45.
    30% → 45
  2. Find 1%. Divide the part by 30, because 30% is 30 lots of 1%.
    45 ÷ 30 = 1.5
  3. Find 100%. The whole is 100%, so multiply the 1% amount by 100.
    1.5 × 100 = 150
  4. Write the answer.
    150

Check. 30% of 150 is 45, which matches the part of 45 in the question. ✓

Watch out. Do not find 30% of 45. The 45 is the part, and we need the whole.

Watch out

Do not find 30% of 45. The 45 is the part, not the whole. When the whole is missing, find 1% first.

Exam tip

Exam tip. Write the amount you know, and the percentage you know, before you start. Then ask: which is the whole?

Exercise 6F  Estimating and solving percentage problems

Non-calculator
1
PSEstimate 52% of 398. Give your estimate.
2
PSEstimate 24% of 49 by using 25% of 48. Give your estimate.
3
PSIs 40% of 150 more or less than 65? Explain your answer.
4
PSA jacket costs £64. In a sale it is 25% off. How much does the customer pay (£)?
5
PSA school has 240 pupils. 25% of them walk to school. Of the pupils who do not walk, 40% ride bikes. How many pupils ride bikes?
6
PS30% of a number is 45. What is the number?
7
PS15% of a number is 12. What is the number?
8
PSA bike costs £220. Ben has saved 60% of the price. How much more (£) does he need?
9
PSFind 4% of 350 g. Give the answer in grams (g).
10
RTom says 35% of 60 is 18. Show how to check him. Is he right?
11
RSam says that 50% of 80 plus 10% of 80 is the same as 60% of 80. Is he right? Explain your answer.
12
RAlways, sometimes or never? When you find 60% of a number, the answer is more than half of the number. Explain your answer.
13
PSA shop has 480 apples. On Monday, 25% of them are sold. On Tuesday, a third of the apples that are left are sold. How many apples are left after Tuesday?

Chapter summary

SkillMethod
Per cent and equivalencesPer cent means out of 100. A decimal becomes a percentage with × 100. A fraction becomes a percentage by making the bottom 100, or by dividing and then × 100.
Building blocks10% is ÷ 10, 1% is ÷ 100, 50% is half, 25% is a quarter, 75% is three quarters. Add the parts for other percentages.
A percentage of a measureWrite the percentage as a fraction out of 100 and multiply, or build it from 10%. Make the units the same first.
A part as a percentage of a wholepart ÷ whole, then × 100. Use the same units on the top and the bottom.
Finding the wholeFind 1% of the whole from the part, then multiply by 100.
ComparingChange each amount to a percentage of its own whole and then compare. For savings, compare the amounts saved in pounds.

Can you…?

  • I can change between fractions, decimals and percentages, including 1/8 = 12.5% and 3/8 = 37.5%.
  • I can find 10%, 1%, 50%, 25% and 75% of an amount.
  • I can find a percentage of a measure, such as 15% of 360.
  • I can write one amount as a percentage of another.
  • I can compare percentages from different totals, and savings in pounds.
  • I can estimate a percentage first, then check my answer.

Key terms

Per cent
Out of 100. The sign % means per cent.
Percentage
A number of parts out of 100. 35% means 35 out of 100.
Equivalent
Having the same value. 1/2, 0.5 and 50% are equivalent.
Part and whole
The part is the amount we are interested in. The whole is the total.
Building block
An easy percentage, such as 10% or 50%, used to find other percentages.
Estimate
A sensible guess found by changing the numbers to easy ones.

Exercise 6Z  Check-up (non-calculator)

Non-calculator
1
What is 65% as a decimal?
2
Write 0.04 as a percentage. Give the number of %.
3
Write 5/8 as a percentage. Give the number of %.
4
Write 3/20 as a percentage. Give the number of %.
5
What is 10% of 470?
6
What is 1% of 900?
7
What is 15% of 360?
8
Find 35% of 80 kg. Give the answer in kilograms (kg).
9
Which is greater, 3/4 or 72%?
10
Mia scored 16 out of 25 in a test. Liam scored 70%. Who scored the higher percentage?

Total 21 marks. Allow about 21 minutes.

Exercise 6X  SATs-style questions

Non-calculator
1
FWrite 0.9 as a percentage. Give the number of %.[1 mark]
2
FWrite 45% as a decimal.[1 mark]
3
FWork out 75% of 64.[1 mark]
4
FWork out 35% of 260. Show your working.[2 marks]
5
FFind 15% of £40. Give your answer in pounds (£). Show your working.[2 marks]
6
FWrite 7/20 as a percentage. Give the number of %. Show your working.[2 marks]
7
FIn a class of 25 pupils, 14 have a pet. What percentage (%) of the class have a pet? Show your working.[2 marks]
8
RSam says that 40% of 150 is greater than 60% of 90. Is he right? Show your working.[3 marks]
9
PSA school has 320 pupils. 30% of them are in Year 6. Of the Year 6 pupils, 25% are in the choir. How many Year 6 pupils are in the choir?[3 marks]
10
PSShop A takes 20% off a £45 jacket. Shop B takes 25% off a £52 jacket. Which shop sells its jacket for less? Show your working.[4 marks]

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