What is 1/5 of 100?

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 100? We'll show you a straightforward method to achieve that.

How to calculate 1/5 of 100?

  1. Multiply the whole number by the numerator of the fraction: 100 × 1 = 100
  2. Divide this result by denominator of the fraction: 100/5 = 20
  3. Simplify by dividing both the numerator and denominator by their GCD (5):
    • 100/5 = 20
    • 5/5 = 1
  4. Which gives: 20/1

How does it work?

The principle behind finding a fraction of a number, such as 1/5 of 100, is rooted in the method of cross-multiplication.

Consider the following proportion: 1 5 = x 100 (where x represents 1/5 of 100)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 1 × 100 = 5 x
  2. Which gives: 100 = 5 x
  3. Divide both sides by 5 to isolate x: 100 5 = 5 x 5
  4. Which gives the result: 100 5 = x (or 20 1 = x )

Thus, 1/5 of 100 is equal to 20/1 (or 20 in its decimal form).