How to Calculate Missing Ratio

Ratios are often used when measuring distances.

A ratio is a way of comparing the sizes of two different numbers. A ratio is closely related to the concept of a proportion, which is an equation that uses ratios to compare the sizes of two different numbers. A proportion is generally used to show two equivalent fractions, or fractions with different forms that represent the same number. In many proportions, there is a missing ratio; that is, a ratio that is equivalent to another ratio, but is incomplete. A missing ratio can be found in a few short steps.

Instructions

1. Write down the proportion to be solved. For example, assume the ratio is given by the following equation:

   x/3 = 4/12

2. Isolate the unknown variable in the proportion. In this example, "x" can be isolated by multiplying both sides of the proportion by 3; this yields:

   x = (3*4)/12

3. Solve the equation for x. Concluding the example, the 3*4 equals 12, and the proportion is therefore:

   x = 12/12 = 1

4. Substitute the variable into the ratio. Substituting 1 into the ratio x/3 gives 1/3. This is the value of the missing ratio.

References

• Purplemath: Proportions: Introduction
• Washington County School Disctrict: Equivalent Fractions