What is 9/8 of 18?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 9/8 of 18? We'll show you a straightforward method to achieve that.

How to calculate 9/8 of 18?

  1. Multiply the whole number by the numerator of the fraction: 18 × 9 = 162
  2. Divide this result by denominator of the fraction: 162/8 = 20.25
  3. Simplify by dividing both the numerator and denominator by their GCD (2):
    • 162/2 = 81
    • 8/2 = 4
  4. Which gives: 81/4

Since 81/4 is an improper fraction, the result could also be expressed as a mixed number: 20 1/4

How does it work?

The principle behind finding a fraction of a number, such as 9/8 of 18, is rooted in the method of cross-multiplication.

Consider the following proportion: 9 8 = x 18 (where x represents 9/8 of 18)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 9 × 18 = 8 x
  2. Which gives: 162 = 8 x
  3. Divide both sides by 8 to isolate x: 162 8 = 8 x 8
  4. Which gives the result: 162 8 = x (or 81 4 = x )

Thus, 9/8 of 18 is equal to 81/4 (or 20.25 in its decimal form).