Question

A.) Multiply these numbers the quickest and easiest way possible: 87 x 5 x 2 B.) Explain how you were able to quickly determine the product. Justify your reasoning using a property of multiplication.

Answer 1

It is easy to multiply numbers by 10: you simply have to add an extra zero at the end.

This means that, using associative property, we know that

$87\times 5 \times 2 = (87\times 5) \times 2 = 87 \times (5\times 2)$

The last expression is the easiest to compute, because we have

$87 \times (5\times 2) = 87 \times 10 = 870$