Write down your two ratios and separate them with an equals sign. Proportion fractions always equal each other. For example, 3/4 = x/20.
Find a common denominator between the two fractions. One way of accomplishing this is to discover a number into which both can evenly divide. Regarding the denominators in the sample problem, they both divide evenly into 20. However, If such a number is not as easy to discover, you may multiply the denominators together to create a common number.
Multiply the numerator by the number used to transform the denominator. In this case, the original proportion was 3/4 = x/20, and the common denominator is 20. Therefore, the denominator as well as the numerator in the first ratio must be multiplied by five to create 15/20.
Finalize your algebraic proportion. After multiplying 3/4 by 5/5, the first proportion is 15/20, making the new proportion 15/20 = x/20. Therefore, the final answer is 3/4 = x/20; x = 15.