What’s the Error? Dominic has 5 books with 12 postcards in each book. He has 4 boxes with 20 coins in each box. If he gives 15 post cards to a friend, how many postcards and coins does he have?
Dominic drew this model.
Dominic used these steps to solve.
5 × 12 + 4 × 20 – 15 = n
60 + 4 × 20 – 15 = n
64 × 20 – 15 = n
1,280 – 15 = n
1,265 = n
Look at the steps Dominic used to solve this problem. Find and describe his error.
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