What is 2/4 of 21?

How to calculate 2/4 of 21?

1. Multiply the whole number by the numerator of the fraction: 21 × 2 = 42
2. Divide this result by denominator of the fraction: 42/4 = 10.5
3. Simplify by dividing both the numerator and denominator by their GCD (2):
   • 42/2 = 21
   • 4/2 = 2
4. Which gives: 21/2

Since 21/2 is an improper fraction, the result could also be expressed as a mixed number: 10 1/2

How does it work?

The principle behind finding a fraction of a number, such as 2/4 of 21, is rooted in the method of cross-multiplication.

Consider the following proportion: $\frac{2}{4}=\frac{x}{21}$ (where x represents 2/4 of 21)

1. Using the cross-multiplication method, multiply both numerators by their opposite denominators: $2\times 21=4x$
2. Which gives: $42=4x$
3. Divide both sides by 4 to isolate x: $\frac{42}{4}=\frac{4x}{4}$
4. Which gives the result: $\frac{42}{4}=x$ (or $\frac{21}{2}=x$)

Thus, 2/4 of 21 is equal to 21/2 (or 10.5 in its decimal form).