Why does my child think 3 − 8 = 5?
Your child gets the right size of answer but the wrong sign, such as 3 - 8 = 5.
Why children do it
Before negative numbers, children learn to take the smaller number from the bigger one, whatever the order, because 3 − 8 "can't be done". The habit stays: they find the right difference, 5, but forget that taking 8 away from 3 goes below zero, to −5.
How to help at home
Ask them to check the sign: taking away a bigger number than you start with goes below zero.
The right way
Calculate: −7 + 10
- 10 − 7Adding 10 to -7 is the same as subtracting 7 from 10.
- 310 is further from zero than -7, so the answer is positive.
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