Why does my child think 3 × 2/5 = 6/15?
Your child multiplies both the top and the bottom by a whole number, such as 3 × 2/5 = 6/15 instead of 6/5.
Why children do it
Children who've learnt to multiply the top and the bottom of a fraction by the same number often do it here too. But 3 × 2/5 means three lots of two fifths, which is six fifths. The pieces are still fifths, so only the top changes. Multiplying the bottom as well just gives 2/5 again, written differently.
How to help at home
Three lots of 2/5 is 6/5: only the top is multiplied, since the size of the parts doesn't change.
The right way
Calculate: 3 × (2/5)
- 6/53 lots of 2 fifths is 6 fifths: multiply the top by 3, and the bottom stays 5.
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