Question

Michael bought 8 new Pokemon cards to add to his collection.

The next day his dog ate half of his collection. There are now only
40 cards left. How many cards did Michael start with?

Answer 1

72

Explanation:

I like to work backward with problems like these. I'll start out with 40. Then it says that his dog ate half of this number. Instead of dividing by 2, I'll have to multiply by two since I'm working backward.

So, now I have 80, the number of cards he had before his dog ate half of the collection. We also see that he bought 8 new Pokemon cards and added these two his collection. Instead of adding 8, I'll subtract 8 from 80, giving me 72. So, this is his original amount.

If I take this number and go back through the scenario, I can check my work.

72 + 8 = 80, 80/2 = 40