In math, a proportion is an equation that shows the relationship between two ratios or fractions that are equal to each other. A ratio is an ordered pair of numbers a and b, written a/b where b does not equal 0. For example, if there is 1 boy and 3 girls, the ratio can be written as 1:3. Proportions are denoted using the symbol "::" or "=". When two sets of given numbers are increasing or decreasing in the same ratio, then the ratios are said to be directly proportional to each other. Proportions can be used to solve problems involving percents, rates, and other mathematical concepts.