Year 6: Reading a pie chart
Part of the Year 6 pie charts, line graphs and the mean chapter. Chapter overview · whole chapter on one page
Reading a pie chart
A pie chart shows how a whole is split into parts. The whole circle stands for the whole thing. Each part is a sector, a slice of the circle.
The whole circle is 360 degrees. It is also 100 per cent. The sectors always add up to the whole, so the per cents in a pie chart add up to 100, and the angles add up to 360.
A bigger sector means a bigger share. A sector that is half the circle is 50 per cent and 180 degrees. A sector that is a quarter is 25 per cent and 90 degrees. You do not need to measure the angles to read the chart. Read the key, which gives each sector its per cent.
Key ideas
- The whole pie is 360 degrees, and it is 100 per cent.
- The sectors add up to the whole: the per cents add to 100, and the angles add to 360.
- Read the key to find the per cent of each sector.
- A quarter of the pie is 25 per cent, and it is 90 degrees.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Find the label in the key and read the per cent next to it.
- Find Car in the key. Each label in the key has its own sector.Car
- Read the per cent next to it. The per cent tells us the share of the whole pie that the car sector is.Car: 20%
- Write the answer. The per cent is out of 100.20
Check. All the per cents in the key add up to 100. ✓
Watch out. Read the per cent, not the size of the sector by eye.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent into a fraction, then take that fraction of 360 degrees.
- Write the per cent as a fraction. Per cent means out of 100.35/100 = 7/20
- Take that fraction of the whole pie. The whole pie is 360 degrees.7/20 × 360 = 126
- Write the answer. The sector is this many degrees.126
Check. 35 per cent of 360 degrees is 126 degrees. ✓
Watch out. Use 360 degrees for the whole pie. Do not use 100 when you want degrees.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent to a fraction out of 100, then simplify it.
- Read the per cent for Swimming. Per cent means out of 100.25 per cent
- Write it as a fraction out of 100. The bottom number is 100 because it is per cent.25/100
- Simplify the fraction. Divide the top and bottom by the same number until you cannot.25/100 = 1/4
Check. 1/4 of the pie is 25 out of 100 per cent. ✓
Watch out. Simplify to the lowest terms. 25/100 is 1/4, not 1/5.
Watch out
Common mistake: reading a sector as a number of degrees when the question asks for a per cent. A sector of 90 degrees is a quarter of the pie, which is 25 per cent. Check the units in the question before you answer.
Exercise 12A Practice: reading a pie chart
Non-calculatorKey words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Find the label in the key and read the per cent next to it.
- Find Walk in the key. Each label in the key has its own sector.Walk
- Read the per cent next to it. The per cent tells us the share of the whole pie that the walking sector is.Walk: 40%
- Write the answer. The per cent is out of 100.40
Check. All the per cents in the key add up to 100. ✓
Watch out. Read the per cent, not the size of the sector by eye.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent into a fraction, then take that fraction of 360 degrees.
- Write the per cent as a fraction. Per cent means out of 100.40/100 = 2/5
- Take that fraction of the whole pie. The whole pie is 360 degrees.2/5 × 360 = 144
- Write the answer. The sector is this many degrees.144
Check. 40 per cent of 360 degrees is 144 degrees. ✓
Watch out. Use 360 degrees for the whole pie. Do not use 100 when you want degrees.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent into a fraction, then take that fraction of 360 degrees.
- Write the per cent as a fraction. Per cent means out of 100.20/100 = 1/5
- Take that fraction of the whole pie. The whole pie is 360 degrees.1/5 × 360 = 72
- Write the answer. The sector is this many degrees.72
Check. 20 per cent of 360 degrees is 72 degrees. ✓
Watch out. Use 360 degrees for the whole pie. Do not use 100 when you want degrees.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent to a fraction out of 100, then simplify it.
- Read the per cent for Bus. Per cent means out of 100.25 per cent
- Write it as a fraction out of 100. The bottom number is 100 because it is per cent.25/100
- Simplify the fraction. Divide the top and bottom by the same number until you cannot.25/100 = 1/4
Check. 1/4 of the pie is 25 out of 100 per cent. ✓
Watch out. Simplify to the lowest terms. 25/100 is 1/4, not 1/5.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. The biggest sector is the one with the biggest per cent.
- Read the per cent for each sector. Compare the sizes using their per cents.Pasta 35%, Jacket potato 25%, Sandwiches 20%, Salad 10%, Wraps 10%
- Find the biggest per cent. The biggest per cent is the biggest sector.biggest = 35%
- Write the answer. This is the sector with that per cent.Pasta
Check. No other sector is 35 per cent. ✓
Watch out. Compare the per cents, not the order in the key.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Change the per cent into a fraction, then take that fraction of 360 degrees.
- Write the per cent as a fraction. Per cent means out of 100.10/100 = 1/10
- Take that fraction of the whole pie. The whole pie is 360 degrees.1/10 × 360 = 36
- Write the answer. The sector is this many degrees.36
Check. 10 per cent of 360 degrees is 36 degrees. ✓
Watch out. Use 360 degrees for the whole pie. Do not use 100 when you want degrees.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Add the per cents, then write the total as a simplified fraction.
- Add the per cents of the sectors. These sectors together make up this per cent of the pie.15 + 10 = 25
- Write the total as a fraction out of 100. Per cent means out of 100.25/100
- Simplify the fraction. Divide the top and bottom by the same number.25/100 = 1/4
Check. 1/4 of the pie is 25 out of 100. ✓
Watch out. Add first, then simplify. Do not simplify each sector and then add them.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Take the football sector away from the whole pie, which is 100 per cent.
- Write the whole pie. The whole pie is 100 per cent.100
- Take away the football sector. The rest of the pie is everyone who did not choose football.100 − 30 = 70
- Write the answer. 70
Check. 70 + 30 = 100. ✓
Watch out. Subtract from 100, because the whole pie is 100 per cent.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Find the label in the key and read the per cent next to it.
- Find Bike in the key. Each label in the key has its own sector.Bike
- Read the per cent next to it. The per cent tells us the share of the whole pie that the bike sector is.Bike: 15%
- Write the answer. The per cent is out of 100.15
Check. All the per cents in the key add up to 100. ✓
Watch out. Read the per cent, not the size of the sector by eye.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Read each per cent and add them together.
- Read the per cent for each sector. We need the sectors for walking and the bus.Walk 40%, Bus 25%
- Add the per cents together. Adding the sectors gives their share of the whole pie.40 + 25 = 65
- Write the answer. This is the per cent for all the sectors together.65
Check. The whole pie is 100 per cent, so the rest of the pie is 35 per cent. ✓
Watch out. Add the per cents, not the degrees. The whole pie is 100 per cent.
Key words. A pie chart shows a whole split into sectors. Each sector is a slice of the circle. The whole pie is 360 degrees, and it is also 100 per cent.
Method. Compare the walking sector with the two sectors for the bus and the bike.
- Read the walking sector. Walking is 40 per cent.Walk = 40%
- Add the bus and the bike. Bus is 25 per cent and bike is 15 per cent.25 + 15 = 40
- Compare the two. Both come to 40 per cent, so they are equal.40 = 40
- Decide. Sam says walking is more, but the two are the same.No, Sam is wrong.
Check. Walking is 40 per cent and bus plus bike is 40 per cent, so neither is bigger. ✓
Watch out. Add the sectors before you compare them with one sector.
Watch out
Watch out: a pie chart does not show how many children there are. It shows the share of each sector. Two sectors with the same size have the same share, even if they have different names.
Exam tip
When you read a pie chart, check that the per cents add up to 100 before you use them.