Glossary
percent change
Percent change measures a change against the starting value: the amount of change divided by the original, then written as a percent.
A percent change states how much a value moved relative to where it started: take the amount of change, divide it by the starting value, and multiply by 100. A dose that goes from 40 mg to 50 mg rose by 10 mg, which is 10 ÷ 40 = 25 percent — not 10 ÷ 50, which would give 20 percent, the figure that follows from dividing by the wrong base. Downward changes work the same way and are reported as a decrease of that size. Two habits avoid most errors. Write the starting value first, before touching the calculator, because the base is the whole of the question and it is easy to reach for the newer number. And check that the answer is plausible: a decrease can never exceed 100 percent, and a rise over 100 percent means the value more than doubled — if the question did not describe that, reread what was actually asked.
Taught in
Related terms
- proportion — A proportion is a statement that two ratios are equal, with one of the four values missing — and the missing value is what the calculation returns.
- decimal — A decimal writes a fraction using place value after a decimal point, so 0.75 means 75 hundredths, and the alignment of that point governs every operation.
- rounding — Rounding replaces a number with a near one at a chosen place value, using the digit after it: five or more rounds up, less than five rounds down.
Source: The math guides in this course (ratio and proportion, measurement and conversion, dosage calculation): every definition and worked value above was written for this course, because arithmetic and unit conversion are not a publisher's prose, and each guide shows the method worked. Elsevier's own HESI A2 page, which names math among the areas the exam covers, is the exam-side source. (Elsevier HESI A2 page accessed 2026-10-23; definitions written 2026-10-27)