Math CentralQuandaries & Queries


Question from Beth, a parent:

Estimate using compatible numbers:

2 X 3978 =

102/25 =


When working with "compatible" numbers, you generally round things off to make the arithmetic easy.

For example, 19 x 202 is about 20 x 200 which is easy: 4000.

The accurate answer for 19 x 202 is 3838, so 4000 is a reasonable estimate.

Another example: 17/63 is about 16/64 which cancels down easily to 1/4.

Stephen La Rocque.

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