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Primary Maths · Year 4Chapter 5 · Fractions
Year 4 · Fractions · Lesson 5.1

Year 4: Fractions of shapes and sets

Part of the Year 4 fractions chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)

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5.1

Fractions of shapes and sets

Year 4
Unit and non-unit fractions of shapes and sets, Parts must be equal

A fraction is a part of a whole. To make a fraction we cut a whole thing into equal parts. Equal means exactly the same size. Think of a pizza cut into 8 equal slices. One slice is one eighth of the pizza.

A fraction has two numbers. The bottom number is the denominator. It tells us how many equal parts there are altogether. The top number is the numerator. It tells us how many of those parts we are talking about.

This bar is cut into 8 equal parts. 3 parts are shaded. The shaded part is three eighths, written 3/8.

38

The top number is the numerator (3 parts shaded). The bottom number is the denominator (8 equal parts).

A fraction with 1 on the top is a unit fraction: 1/2, 1/3, 1/4, 1/5... A fraction with any other number on the top, like 3/4 or 5/8, is a non-unit fraction. Three quarters is just three unit fractions of one quarter.

   14141414
3/4 is made of three parts, and each part is 1/4.

Fractions of a set. A fraction can also describe a group of things. Here are 8 counters. 3 are red. The fraction of the counters that are red is 3 out of 8, which is 3/8. The bottom number is the whole set (all 8 counters).

RRRBBBBB
3 of the 8 counters are red: the fraction is 3/8.

The parts must be equal. If the parts are different sizes, we cannot name them with a fraction like this.

This rectangle has 4 parts, but they are NOT equal. The shaded part is not one quarter.

Key words. The denominator is the bottom number. The numerator is the top number. A unit fraction has 1 on the top. A non-unit fraction has a top number that is not 1.

Key ideas

  • The bottom number (denominator) = how many equal parts in the whole.
  • The top number (numerator) = how many parts we are talking about.
  • The parts MUST be equal in size.
  • A unit fraction has 1 on the top: 1/5. A non-unit fraction does not: 3/5.
  • For a set, the bottom number is the number of things in the whole set.
  • All the parts together make 1 whole: 8/8 = 1.
Worked example 5.1.1
What fraction of the bar is shaded?

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. A fraction describes equal parts of a whole. Count all the equal parts for the bottom number. Count the parts you want for the top number.

  1. Count ALL the equal parts in the whole. The bottom number of a fraction (the denominator) tells us how many equal parts there are altogether.
    There are 8 equal parts. The denominator is 8.
  2. Count the parts that are shaded. The top number (the numerator) tells us how many parts we are talking about.
    3 parts are shaded. The numerator is 3.
  3. Write the fraction. Put the numerator on top and the denominator on the bottom.
    38   (say “three eighths”)

Check. The parts that are shaded and the other parts together make all 8 parts: 3 + 5 = 8. ✓

Watch out. Count ALL the parts for the bottom number, not just the white ones.

Worked example 5.1.2
What fraction of the circle is shaded?

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. A fraction describes equal parts of a whole. Count all the equal parts for the bottom number. Count the parts you want for the top number.

  1. Count ALL the equal parts in the whole. The bottom number of a fraction (the denominator) tells us how many equal parts there are altogether.
    There are 8 equal parts. The denominator is 8.
  2. Count the parts that are shaded. The top number (the numerator) tells us how many parts we are talking about.
    5 parts are shaded. The numerator is 5.
  3. Write the fraction. Put the numerator on top and the denominator on the bottom.
    58   (say “five eighths”)

Check. The parts that are shaded and the other parts together make all 8 parts: 5 + 3 = 8. ✓

Watch out. Count ALL the parts for the bottom number, not just the white ones.

Worked example 5.1.3
What fraction of the hexagon is not shaded?

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. Count all the equal parts for the bottom number. Count the parts that are NOT shaded for the top number.

  1. Count ALL the equal parts. This is the bottom number (denominator).
    There are 6 equal parts altogether.
  2. Count the parts that are NOT shaded. These are the white parts.
    6 − 5 = 1. So 1 part is not shaded.
  3. Write the fraction. The white parts go on the top. The total number of parts goes on the bottom.
    16

Check. Shaded + not shaded: 56 + 16 = 66 = 1 whole. ✓

Watch out. The question asks for the parts that are not shaded, so count the white ones.

Worked example 5.1.4
A bag has 3 red counters, 4 blue counters and 2 green counters. What fraction of the counters are blue?
RRRBBBBGG

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. A fraction of a set compares the part with the whole set. The total goes on the bottom and the part you want goes on the top.

  1. Count ALL the counters. The total goes on the bottom of the fraction.
    red: 3
    blue: 4
    green: 2
    Total: 3 + 4 + 2 = 9
  2. Count the blue counters. This number goes on the top of the fraction.
    There are 4 blue counters.
  3. Write the fraction. 4 out of 9 is the fraction 4/9.
    49   (say “four ninths”)

Check. Add the fractions of every colour: the tops add up to 9, so the fractions together make 99 = 1 whole. ✓

Watch out. The bottom number is the whole set (9), not the number of the other colours.

Worked example 5.1.5
15 counters are put into 5 equal groups. 3 of the groups are coloured red. What fraction of the groups are coloured?

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. A fraction describes equal parts of a whole. Count all the equal parts for the bottom number. Count the parts you want for the top number.

  1. Count ALL the equal parts in the whole. The bottom number of a fraction (the denominator) tells us how many equal parts there are altogether.
    There are 5 equal groups. The denominator is 5.
  2. Count the groups that are coloured. The top number (the numerator) tells us how many parts we are talking about.
    3 groups are coloured. The numerator is 3.
  3. Write the fraction. Put the numerator on top and the denominator on the bottom.
    35   (say “three fifths”)

Check. The parts that are coloured and the other parts together make all 5 parts: 3 + 2 = 5. ✓

Watch out. Count ALL the parts for the bottom number, not just the white ones.

Worked example 5.1.6
Shade 5/6 of the shape. How many parts do you shade?

Key words. The denominator (bottom number) is how many equal parts. The numerator (top number) is how many parts we have.

Method. The bottom number tells us how many equal parts the whole is cut into. The top number tells us how many to shade.

  1. Look at the bottom number of 56. It is 6, so the whole must be cut into 6 equal parts.
    The picture has 6 equal parts. ✓
  2. Look at the top number. This is how many parts to shade.
    The top number is 5.
  3. Write the answer.
    Shade 5 of the 6 parts.

Check. Count again: 5 shaded and 1 white make 6 parts. ✓

Watch out. The bottom number is the total number of parts. Do not shade that many!

Worked example 5.1.7
Aisha says, “The shaded part is one quarter, because the rectangle has 4 parts.” Is she right?

Method. A fraction needs equal parts. Look at whether the parts are the same size.

  1. Count the parts. There are 4 parts.
    The rectangle has 4 parts.
  2. Check the sizes. The parts are not the same width. The shaded part is much smaller than the longest part.
  3. Decide. To be “one quarter” the whole must be cut into 4 EQUAL parts.
    No. The parts are not equal, so the shaded part is not 1/4.

Check. If the 4 parts were equal, each would be the same width as the shaded one. They are not. ✓

Watch out. Do not just count the parts. Check that they are equal.

Watch out

The parts must be equal. A shape cut into 4 parts is not always cut into quarters. Check that the parts are the same size. Also remember: the bottom number is the number of parts in the whole, not the number of parts you can see shaded or the number of white parts.

Exercise 5A  Fractions of shapes and sets

Non-calculator
1
FWhat fraction of each shape is shaded?
(a)
 
(b)
 
(c)
 
(d)
 
(e)
 
(f)
 
2
FWrite each of these as a fraction with numbers.
(a)three quarters =
(b)two fifths =
(c)five eighths =
(d)seven tenths =
(e)one sixth =
(f)two thirds =
3
FWrite each fraction in words.
(a)14 =
(b)23 =
(c)56 =
(d)38 =
(e)910 =
(f)45 =
4
FHow many parts must be shaded to show each fraction? The shapes are not shaded yet.
(a)
Shade 35. How many parts?
(b)
Shade 58. How many parts?
(c)
Shade 710. How many parts?
5
FWhat fraction of each shape is not shaded?
(a)
 
(b)
 
(c)
 
(d)
 
6
FWhat fraction of the counters are the colour in the question?
(a)
RRRBBBBB
What fraction of the counters are red?
(b)
GGGGGGGYYY
What fraction of the counters are yellow?
(c)
RRBBBBGGG
What fraction of the counters are blue?
(d)
YYYYYPPPPPP
What fraction of the counters are purple?
7
FThe counters are in equal groups. Some groups are coloured red. What fraction of the groups are red?
(a)
Fraction of groups that are red =
(b)
Fraction of groups that are red =
(c)
Fraction of groups that are red =
8
PSA pizza is cut into 8 equal slices. Noah eats 3 slices. Mei eats 1 slice.
(a)What fraction of the pizza does Noah eat?
(b)What fraction of the pizza does Mei eat?
(c)What fraction of the pizza is not eaten by Noah?
9
RWhich two pictures show one quarter shaded? Tick two boxes.
A
B
C
D
E
10
RWhich fraction is the odd one out?   12    13    34    15.   Explain.
11
RAlways, sometimes or never?   When a shape is cut into 4 parts, each part is one quarter.
12
RLeo says, “13 of the rectangle is shaded, because there are 3 parts and 1 is shaded.” Is Leo right? Explain.
13
RA rectangle is cut into 12 equal squares. 3 squares are blue and 4 squares are yellow. The rest are white. What fraction of the squares are white?

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