What is 1/2 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 1/2 of 21? We'll show you a straightforward method to achieve that.

How to calculate 1/2 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: 21/2 = 10.5

Since 21/2 is an improper fraction, the result could also be expressed as a mixed number: 10 1/2

How does it work?

The principle behind finding a fraction of a number, such as 1/2 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: 1 2 = x 21 (where x represents 1/2 of 21)

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

Thus, 1/2 of 21 is equal to 21/2 (or 10.5 in its decimal form).