Subtracting fractions · Year 8
In Year 8 you learn: subtracting fractions in problems.
You can only subtract fractions when the pieces are the same size, so the denominators must match. If they don’t, change them to a common denominator first. With mixed numbers you may need to exchange a whole for fraction pieces.
Key facts
- Different denominators: first change both to a common denominator (the lowest common multiple is easiest). Then add or subtract.
- When subtracting mixed numbers you may need to exchange a whole: 4 1/5 = 3 6/5.
Worked examples
Example 1
Work out 4/5 − 1/3.
Answer: 7/15
Example 2
Sipho earns £12,000 a month. He spends 1/4 of it on rent and 1/3 on food. How much is left?
Answer: £5,000
Example 3
Work out 3 1/4 − 1 2/3.
Answer: 1 7/12
Example 4
Work out 5 1/3 − 2 3/4.
Answer: 2 7/12
Example 5
A ribbon is 4 1/2 m long. Mia cuts off 1 5/6 m. How much ribbon is left?
Answer: 2 2/3 m