Elementary Algebra

In order to add rational numbers with a common denominator, we simply add the numerators and place the result over the common denominator. This works because fractions with the same denominator express different amounts of parts out of the same total amount of parts. For example, one slice, or $\frac{1}{8}$ of a pizza plus two slices, or $\frac{2}{8}$ of a pizza is equal to three slices, or $\frac{3}{8}$ of a pizza.