Proportion Formula
Before we begin with the proportion formula, let us first recall the concept of proportion. Any equation is said to be in proportion when the elements in them are in proportion. That means if the elements in an equation are a, b, c, and d, then the equation would be in proportion when a, b, c, and d are in proportion. The elements a and d are called extremes, while b and c are called mean terms. In the ratio, the product of means equals the product of extremes. Any two ratios are said to be equal if their crossproducts are equal. Let us understand proportion formula using solved examples.
What is Proportion Formula?
According to the definition of proportion, when two ratios are equivalent, they are in proportion. The proportion formula is used to depict that two ratios or fractions are equal. The proportion formula can be given as,
a : b :: c : d = a/b = c/d
where,
 a, d = Extreme terms
 b, c = Mean terms
Let us now look at a few solved examples on the proportion formula to understand the concept better.
Solved Examples Using Proportion Formula

Example 1: What is the value of x in 12 : x :: 4 : 5?
Solution:
To find: Value of x in the given equation.
Using the proportion formula,
a : b :: c : d = a/b = c/d
12/x = 4/5
x = 15
Answer: Value of x = 15

Example 2: Sam runs 6 miles in 30 minutes. At this rate, how far could he run in 45 minutes?
Solution:
To find: Distance covered by Sam in 45 minutes.
Let us assume the unknown quantity here to be x.
Using the proportion formula,
6 : 30 :: x : 45 = 6/30 = x/45
x = 9 miles
Answer: Therefore, the distance covered by Sam in 45 mins = 9 miles.