It can be written in two ways: as two equal fractions a/b = c/d; or using a colon, a:b = c:d. The following proportion is read as "twenty is to twenty-five as four is to five." In problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion.
20/25 = 4/5
20 x 5 = 25 x 4
100 = 100