What is 4/8 of 21?
Often, in mathematics or everyday life, we need to find a fraction of a given number. For instance, how would you quickly calculate 4/8 of 21? We'll show you a straightforward method to achieve that.
How to calculate 4/8 of 21?
- Multiply the whole number by the numerator of the fraction: 21 × 4 = 84
- Divide this result by denominator of the fraction: 84/8 = 10.5
- Simplify by dividing both the numerator and denominator by their GCD (4):
- 84/4 = 21
- 8/4 = 2
- 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 4/8 of 21, is rooted in the method of cross-multiplication.
Consider the following proportion: (where x represents 4/8 of 21)
- Using the cross-multiplication method, multiply both numerators by their opposite denominators:
- Which gives:
- Divide both sides by 8 to isolate x:
- Which gives the result: (or )
Thus, 4/8 of 21 is equal to 21/2 (or 10.5 in its decimal form).