What is 3/10 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 3/10 of 42? We'll show you a straightforward method to achieve that.

How to calculate 3/10 of 42?

  1. Multiply the whole number by the numerator of the fraction: 42 × 3 = 126
  2. Divide this result by denominator of the fraction: 126/10 = 12.6
  3. Simplify by dividing both the numerator and denominator by their GCD (2):
    • 126/2 = 63
    • 10/2 = 5
  4. Which gives: 63/5

Since 63/5 is an improper fraction, the result could also be expressed as a mixed number: 12 3/5

How does it work?

The principle behind finding a fraction of a number, such as 3/10 of 42, is rooted in the method of cross-multiplication.

Consider the following proportion: 3 10 = x 42 (where x represents 3/10 of 42)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 3 × 42 = 10 x
  2. Which gives: 126 = 10 x
  3. Divide both sides by 10 to isolate x: 126 10 = 10 x 10
  4. Which gives the result: 126 10 = x (or 63 5 = x )

Thus, 3/10 of 42 is equal to 63/5 (or 12.6 in its decimal form).