What is 1/7 of 21?

How to calculate 1/7 of 21?

1. Multiply the whole number by the numerator of the fraction: 21 × 1 = 21
2. Divide this result by denominator of the fraction: 21/7 = 3
3. Simplify by dividing both the numerator and denominator by their GCD (7):
   • 21/7 = 3
   • 7/7 = 1
4. Which gives: 3/1

How does it work?

The principle behind finding a fraction of a number, such as 1/7 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: $\frac{1}{7}=\frac{x}{21}$ (where x represents 1/7 of 21)

1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: $1\times 21=7x$
2. Which gives: $21=7x$
3. Divide both sides by 7 to isolate x: $\frac{21}{7}=\frac{7x}{7}$
4. Which gives the result: $\frac{21}{7}=x$ (or $\frac{3}{1}=x$)

Thus, 1/7 of 21 is equal to 3/1 (or 3 in its decimal form).