It’s September and kids are going back to school. They meet new friends, new teachers, and challenges of learning new concepts. As a parent, I often get questions from my kids. But they ask questions that stump us sometimes.

For example, how do you explain when you subtract a negative number, you get a number bigger than you started? 1 – ( – 5 ) = 6 as an example. Mechanically I understand how to compute it. But how do I explain this to a child who is trying to understand why?

Stumped? It stumped me. I thought about using a timeline to show an example. Also I thought about using temperature as an example. None really worked until I finally came up with one that worked. Here’s how I explained it.

At a grocery store, you see an in-store coupon for a box of ice cream. The regular price is $9.99 but with the coupon, you get $2 off, or -$2 from the regular price. When you ADD (+) the coupon, the resulting price is lower than you started: $9.99 +  (-$2.00) = $7.99. At the cash register, you realize you lost the coupon. You thought you would only pay $7.99. But now you TAKE AWAY (-) the coupon, you will pay $2.00 more: $7.99 – (-$2.00) = $9.99.

I hope this example is helpful. You may also have good examples to share. If you do, please share it in the comment section. In my next post, I will explain how to give examples of negative multiplications and divisions.