Calculate the Greatest Common Factor or GCF of 21, 45, 72 and 84
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The instructions to find the GCF of 21, 45, 72 and 84 are the next:
1. Decompose all numbers into prime factors
| 21 | 3 |
| 7 | 7 |
| 1 |
| 45 | 3 |
| 15 | 3 |
| 5 | 5 |
| 1 |
| 72 | 2 |
| 36 | 2 |
| 18 | 2 |
| 9 | 3 |
| 3 | 3 |
| 1 |
| 84 | 2 |
| 42 | 2 |
| 21 | 3 |
| 7 | 7 |
| 1 |
2. Write all numbers as the product of its prime factors
| Prime factors of 21 | = | 3 . 7 |
| Prime factors of 45 | = | 32 . 5 |
| Prime factors of 72 | = | 23 . 32 |
| Prime factors of 84 | = | 22 . 3 . 7 |
3. Choose the common prime factors with the lowest exponent
Common prime factors: 3
Common prime factors with the lowest exponent: 31
4. Calculate the Greatest Common Factor or GCF
Remember, to find the GCF of several numbers you must multiply the common prime factors with the lowest exponent.
GCF = 31 = 3
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