What is 4/10 of 87?

Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 4/10 of 87? We'll show you a straightforward method to achieve that.

How to calculate 4/10 of 87?

  1. Multiply the whole number by the numerator of the fraction: 87 × 4 = 348
  2. Divide this result by denominator of the fraction: 348/10 = 34.8
  3. Simplify by dividing both the numerator and denominator by their GCD (2):
    • 348/2 = 174
    • 10/2 = 5
  4. Which gives: 174/5

Since 174/5 is an improper fraction, the result could also be expressed as a mixed number: 34 4/5

How does it work?

The principle behind finding a fraction of a number, such as 4/10 of 87, is rooted in the method of cross-multiplication.

Consider the following proportion: 4 10 = x 87 (where x represents 4/10 of 87)

  1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: 4 × 87 = 10 x
  2. Which gives: 348 = 10 x
  3. Divide both sides by 10 to isolate x: 348 10 = 10 x 10
  4. Which gives the result: 348 10 = x (or 174 5 = x )

Thus, 4/10 of 87 is equal to 174/5 (or 34.8 in its decimal form).