What is 5/7 of 81?

How to calculate 5/7 of 81?

1. Multiply the whole number by the numerator of the fraction: 81 × 5 = 405
2. Divide this result by denominator of the fraction: 405/7 = 57.857142857143

Since 405/7 is an improper fraction, the result could also be expressed as a mixed number: 57 6/7

How does it work?

The principle behind finding a fraction of a number, such as 5/7 of 81, is rooted in the method of cross-multiplication.

Consider the following proportion: $\frac{5}{7}=\frac{x}{81}$ (where x represents 5/7 of 81)

1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: $5\times 81=7x$
2. Which gives: $405=7x$
3. Divide both sides by 7 to isolate x: $\frac{405}{7}=\frac{7x}{7}$
4. Which gives the result: $\frac{405}{7}=x$

Thus, 5/7 of 81 is equal to 405/7 (or 57.857142857143 in its decimal form).