Has your kid been introduced to negative integers? You should compare positive integers to money in your wallet et negative ones to debt when the wallet becomes empty.

After that, you should explain him that when you add the same integer to the 2 sides of an equality you still have an equality.

So, if 14 - 27 = 13 then 14 - 27 + 27 = 13 + 27 and 14 = 40 is wrong.

But, if 14 - 27 = -13 then 14 - 27 + 27 = -13 + 27 and 14 = 14 is correct.

Good luck!

JeanMarie