Answer the following question, with explanation first.
John has 3 children. He and his wife are supposed to buy notebooks for their sons but they couldn't agree on how many to buy. So John bought 2 notebooks for each of his children and John's wife bought 5 notebooks for each of them. How many notebooks did they buy in total for their children?

21
John bought 2 notebooks for his 3 children: 2 notebooks / child x 3 children = 6 notebooks.

The father bought 6 notebooks.

John's wife bought 5 notebooks for their three children: 5 notebooks / child x 3 children = 15 notebooks.

The mother bought 15 notebooks.

Now, the total number of notebooks is 6 notebooks + 15 notebooks = 21 notebooks.

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Therefore, the answer is 21