The ratio is an important mathematical concept that allows you to relate two or more quantities, often large, in a simplistic way. A ratio itself is composed of numbers written in a certain order and separated by colons; ratio calculation is similarly straightforward. Typically, you will simplify a ratio by dividing all the numbers by the greatest common divisor.

Define the order of the ratio. Adhere to the order asked in the problem, if possible. For example, if you are calculating the ratio of blue, brown and green eye colors among students in a class, you must write the amounts in the same order as the ratio that you wish to find, such as blue:brown:green.

Write down the numbers involved in the problem in the same fixed order. If you found 15 blue-eyed students, 20-brown eyed students and 10 green-eyed students, write the ratio as 15:20:10.

Simplify the ratio via division. Find the greatest common divisor and divide each number in the ratio by that number. The greatest common divisor is the number that can divide each number without leaving a remainder. For the eye-color example, it is 5, as 5 can divide 15, 20 and 10. Thus, the equivalent ratio is 15/5:20/5:10/5 or 3:4:2.