Why does my child think −7 + 3 = −10?
Your child adds the sizes of a negative and a positive number, such as -7 + 3 = -10, instead of finding the difference.
Why children do it
With a negative and a positive number, the two pull in opposite directions, so the answer is the difference between their sizes, not their sum. Children who see two numbers and a plus sign add the sizes and keep the minus, because that's what adding has always meant. On a number line, −7 + 3 starts at −7 and moves 3 to the right, to −4.
How to help at home
Ask whether the answer should be closer to zero than the numbers in the question. With different signs, it is.
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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