The four percentage questions that cover 99% of real life — including the reverse one everyone gets wrong (a 12% increase is undone by dividing, not subtracting).
What is X% of Y?
%
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X is what % of Y?
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% change from A to B — the variance question
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Reverse: what was it before the change? — the one everyone gets wrong
%
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If something rose 12% to 450,000 it was not 450,000 − 12%. It was 450,000 ÷ 1.12. Use a negative % for decreases.
These tools are provided as they are, for working things out. They are not part of Aether's audited model engine and their results are not checked against it. Satisfy yourself that a number is right before you rely on it.