What is 1/5 of 20?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 1/5 of 20? We'll show you a straightforward method to achieve that.

How to calculate 1/5 of 20?

  1. Multiply the whole number by the numerator of the fraction: 20 × 1 = 20
  2. Divide this result by denominator of the fraction: 20/5 = 4
  3. Simplify by dividing both the numerator and denominator by their GCD (5):
    • 20/5 = 4
    • 5/5 = 1
  4. Which gives: 4/1

How does it work?

The principle behind finding a fraction of a number, such as 1/5 of 20, is rooted in the method of cross-multiplication.

Consider the following proportion: 1 5 = x 20 (where x represents 1/5 of 20)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 1 × 20 = 5 x
  2. Which gives: 20 = 5 x
  3. Divide both sides by 5 to isolate x: 20 5 = 5 x 5
  4. Which gives the result: 20 5 = x (or 4 1 = x )

Thus, 1/5 of 20 is equal to 4/1 (or 4 in its decimal form).