Percent change
SAT glossary · Math
Definition
(new - old)/(old) × 100. The denominator is ALWAYS the original value — that is the entire content of the formula and it is what students get wrong.
Percent change in plain English
Percent change measures how much something has grown or shrunk relative to where it STARTED, using the formula (new-old)/(old)×100. The single most important thing about this formula — and the part students get wrong most often — is that the denominator is ALWAYS the ORIGINAL (old) value, never the new one, and never some other reference point. Get that denominator wrong, and the whole calculation falls apart, even if every other step was done correctly.
Learn these first
Sign up free: all 157 SAT terms as flashcards, plus practice questions with full explanations →