What is 8/4 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 8/4 of 21? We'll show you a straightforward method to achieve that.
How to calculate 8/4 of 21?
- Multiply the whole number by the numerator of the fraction: 21 × 8 = 168
- Divide this result by denominator of the fraction: 168/4 = 42
- Simplify by dividing both the numerator and denominator by their GCD (4):
- 168/4 = 42
- 4/4 = 1
- Which gives: 42/1
How does it work?
The principle behind finding a fraction of a number, such as 8/4 of 21, is rooted in the method of cross-multiplication.
Consider the following proportion: (where x represents 8/4 of 21)
- Using the cross-multiplication method, multiply both numerators by their opposite denominators:
- Which gives:
- Divide both sides by 4 to isolate x:
- Which gives the result: (or )
Thus, 8/4 of 21 is equal to 42/1 (or 42 in its decimal form).