What is 3/10 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 3/10 of 21? We'll show you a straightforward method to achieve that.

How to calculate 3/10 of 21?

  1. Multiply the whole number by the numerator of the fraction: 21 × 3 = 63
  2. Divide this result by denominator of the fraction: 63/10 = 6.3

Since 63/10 is an improper fraction, the result could also be expressed as a mixed number: 6 3/10

How does it work?

The principle behind finding a fraction of a number, such as 3/10 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: 3 10 = x 21 (where x represents 3/10 of 21)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 3 × 21 = 10 x
  2. Which gives: 63 = 10 x
  3. Divide both sides by 10 to isolate x: 63 10 = 10 x 10
  4. Which gives the result: 63 10 = x

Thus, 3/10 of 21 is equal to 63/10 (or 6.3 in its decimal form).