Subtracting fractions, step by step
Taking one fraction from another hits the same wall as adding them.
The question
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same size:40ths
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12÷4=3
40÷4=10
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- Eighths and fifths are different sizes of piece. Two different sizes cannot be counted as one total — that is the whole difficulty here.
- Both can be cut into 40ths: 8 goes into 40, and so does 5. So 40 is the size to use.
- 4/8 is the same amount as 20/40, and 1/5 is the same amount as 8/40. Nothing has got bigger — the pieces just got smaller and there are more of them.
- Now they are the same size, so count them: 20 − 8 = 12, giving 12/40.
- 12/40 written in the biggest pieces it will go into is 3/10.
How it works.
- 01
Eighths and fifths are different sizes of piece. Two different sizes cannot be counted as one total — that is the whole difficulty here.
- 02
Both can be cut into 40ths: 8 goes into 40, and so does 5. So 40 is the size to use.
- 03
4/8 is the same amount as 20/40, and 1/5 is the same amount as 8/40. Nothing has got bigger — the pieces just got smaller and there are more of them.
- 04
Now they are the same size, so count them: 20 − 8 = 12, giving 12/40.
- 05
12/40 written in the biggest pieces it will go into is 3/10.