Glossary
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.
A proportion is a statement that two ratios are equal: 2 mg is to 1 mL as 6 mg is to an unknown number of milliliters. Three of the four values are known and the fourth is what the calculation returns. The setup decides whether the answer is right. Put the same noun in the same position on both sides — milligrams over milliliters on the left means milligrams over milliliters on the right — and write the units beside the numbers rather than trusting memory. With the proportion set, cross-multiplying gives an equation with one unknown: multiply the numerator of one side by the denominator of the other, then divide by the coefficient left on the unknown. Read the question again before writing the answer, because a proportion always returns a number and only the question says what that number is. If the two sides should grow together, the proportion is direct; if one should shrink as the other grows, it is inverse, and the setup has to say so.
Taught in
Related terms
- unit rate — A unit rate is a rate reduced to one unit — dollars per item, kilometers per hour, milligrams per milliliter — which is what makes two offers comparable.
- drop factor — A drop factor is the number of drops an intravenous set delivers per milliliter, printed on the set's packaging, and it is what turns a volume into a drop count.
- ratio — A ratio compares two quantities, written a : b, and it stays the same when both sides are multiplied or divided by the same number.
- cross multiplication — Cross multiplication solves a proportion by multiplying each numerator by the opposite denominator, then dividing by the remaining number.
- reconstitution — Reconstitution is dissolving a powdered medication with a stated volume of diluent so the vial holds a known concentration, which then feeds the proportion.
- percent change — Percent change measures a change against the starting value: the amount of change divided by the original, then written as a percent.
- IV rate — An IV rate is the volume an infusion delivers per hour, found by dividing the total volume by the number of hours it runs.
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)