Make the base visible.

“15% of 80,” “15 is what percent of 80,” and “from 80 to 15” are different questions. Choose the one you mean.

A QUICK DISTINCTION

A move from 20% to 25% is an increase of 5 percentage points. Relative to the original 20%, the change is 25%. One compares rates by subtraction; the other divides that difference by the starting rate.

CHECK YOUR BASE

Percentages are ratios. Before copying a result, write down what counts as the “whole” or starting amount. The same two values can answer different questions depending on that base.

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