Glossary
denominator
The denominator is the bottom number of a fraction: how many equal parts the whole is divided into, and therefore the size of each part.
The denominator is the bottom number of a fraction and it names the size of the parts: in 3/4 the four says the whole was cut into four equal pieces. That makes it the number that must match before fractions can be added or subtracted, since a third and a quarter are different-sized pieces and cannot be counted together until both are expressed in a common unit. The least common denominator is the smallest number both denominators divide into, and multiplying the two denominators together is a reliable fallback that simply leaves more canceling at the end. A denominator of zero is undefined, because you cannot cut something into no pieces. In unit conversion the denominator usually carries the unit being canceled: write the fraction so the unwanted unit sits opposite the one you are replacing.
Taught in
Related terms
- numerator — The numerator is the top number of a fraction: how many of the equal parts named by the denominator are being counted.
- least common denominator — The least common denominator is the smallest number that both denominators divide into evenly, and it is the shared bottom number used to add or subtract fractions.
- 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.
- mixed number — A mixed number combines a whole number and a proper fraction, such as 1 1/2, and is converted to an improper fraction before multiplying or dividing.
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)