What is 1/8 of 21?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 1/8 of 21? We'll show you a straightforward method to achieve that.

How to calculate 1/8 of 21?

  1. Multiply the whole number by the numerator of the fraction: 21 × 1 = 21
  2. Divide this result by denominator of the fraction: 21/8 = 2.625

Since 21/8 is an improper fraction, the result could also be expressed as a mixed number: 2 5/8

How does it work?

The principle behind finding a fraction of a number, such as 1/8 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: 1 8 = x 21 (where x represents 1/8 of 21)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 1 × 21 = 8 x
  2. Which gives: 21 = 8 x
  3. Divide both sides by 8 to isolate x: 21 8 = 8 x 8
  4. Which gives the result: 21 8 = x

Thus, 1/8 of 21 is equal to 21/8 (or 2.625 in its decimal form).