What is 9/4 of 90?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 9/4 of 90? We'll show you a straightforward method to achieve that.

How to calculate 9/4 of 90?

  1. Multiply the whole number by the numerator of the fraction: 90 × 9 = 810
  2. Divide this result by denominator of the fraction: 810/4 = 202.5
  3. Simplify by dividing both the numerator and denominator by their GCD (2):
    • 810/2 = 405
    • 4/2 = 2
  4. Which gives: 405/2

Since 405/2 is an improper fraction, the result could also be expressed as a mixed number: 202 1/2

How does it work?

The principle behind finding a fraction of a number, such as 9/4 of 90, is rooted in the method of cross-multiplication.

Consider the following proportion: 9 4 = x 90 (where x represents 9/4 of 90)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 9 × 90 = 4 x
  2. Which gives: 810 = 4 x
  3. Divide both sides by 4 to isolate x: 810 4 = 4 x 4
  4. Which gives the result: 810 4 = x (or 405 2 = x )

Thus, 9/4 of 90 is equal to 405/2 (or 202.5 in its decimal form).