What is 8/5 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 8/5 of 21? We'll show you a straightforward method to achieve that.

How to calculate 8/5 of 21?

  1. Multiply the whole number by the numerator of the fraction: 21 × 8 = 168
  2. Divide this result by denominator of the fraction: 168/5 = 33.6

Since 168/5 is an improper fraction, the result could also be expressed as a mixed number: 33 3/5

How does it work?

The principle behind finding a fraction of a number, such as 8/5 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: 8 5 = x 21 (where x represents 8/5 of 21)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 8 × 21 = 5 x
  2. Which gives: 168 = 5 x
  3. Divide both sides by 5 to isolate x: 168 5 = 5 x 5
  4. Which gives the result: 168 5 = x

Thus, 8/5 of 21 is equal to 168/5 (or 33.6 in its decimal form).