What is 9/10 of 42?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 9/10 of 42? We'll show you a straightforward method to achieve that.

How to calculate 9/10 of 42?

  1. Multiply the whole number by the numerator of the fraction: 42 × 9 = 378
  2. Divide this result by denominator of the fraction: 378/10 = 37.8
  3. Simplify by dividing both the numerator and denominator by their GCD (2):
    • 378/2 = 189
    • 10/2 = 5
  4. Which gives: 189/5

Since 189/5 is an improper fraction, the result could also be expressed as a mixed number: 37 4/5

How does it work?

The principle behind finding a fraction of a number, such as 9/10 of 42, is rooted in the method of cross-multiplication.

Consider the following proportion: 9 10 = x 42 (where x represents 9/10 of 42)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 9 × 42 = 10 x
  2. Which gives: 378 = 10 x
  3. Divide both sides by 10 to isolate x: 378 10 = 10 x 10
  4. Which gives the result: 378 10 = x (or 189 5 = x )

Thus, 9/10 of 42 is equal to 189/5 (or 37.8 in its decimal form).