What is 4/9 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 4/9 of 21? We'll show you a straightforward method to achieve that.
How to calculate 4/9 of 21?
- Multiply the whole number by the numerator of the fraction: 21 × 4 = 84
- Divide this result by denominator of the fraction: 84/9 = 9.3333333333333
- Simplify by dividing both the numerator and denominator by their GCD (3):
- 84/3 = 28
- 9/3 = 3
- Which gives: 28/3
Since 28/3 is an improper fraction, the result could also be expressed as a mixed number: 9 1/3
How does it work?
The principle behind finding a fraction of a number, such as 4/9 of 21, is rooted in the method of cross-multiplication.
Consider the following proportion: (where x represents 4/9 of 21)
- Using the cross-multiplication method, multiply both numerators by their opposite denominators:
- Which gives:
- Divide both sides by 9 to isolate x:
- Which gives the result: (or )
Thus, 4/9 of 21 is equal to 28/3 (or 9.3333333333333 in its decimal form).