Compare the size of a product to the size of one factor on the basis of the size of the other factor, without performing the indicated multiplication. For example, the prod- ucts of expressions such as 5 x 3 or 1⁄2 x 3 can be interpreted in terms of a quantity, three, and a scaling factor, five or 1⁄2. Thus in addition to knowing that 5 x 3 = 15, they can also say that 5 x 3 is five times as big as three, without evaluating the product. Likewise they see 1⁄2 x 3 as half the size of three.

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