Percentage Calculator
Three separate questions, one page: X% of Y, X is what percent of Y, and the change from X to Y.
A% of B
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A is what % of B
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Change from A to B
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Worked example
With A = 25 and B = 200: 25% of 200 is 50, 25 is 12.5% of 200, and going from 25 to 200 is a 700% increase.
Percentage questions come in three shapes and people routinely apply the wrong one. "25% of 200" is a multiplication. "25 is what percent of 200" is a division. "From 25 to 200" is a change relative to the starting value — and the last one is where sign errors happen.
The change formula
The change is (new − old) / |old|. Dividing by the absolute value keeps the sign meaningful when the starting point is negative: going from −50 to −25 is an increase, even though the number got closer to zero.