Calculate the Greatest Common Factor or GCF of 21, 77 and 91
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The instructions to find the GCF of 21, 77 and 91 are the next:
1. Decompose all numbers into prime factors
| 21 | 3 |
| 7 | 7 |
| 1 |
| 77 | 7 |
| 11 | 11 |
| 1 |
| 91 | 7 |
| 13 | 13 |
| 1 |
2. Write all numbers as the product of its prime factors
| Prime factors of 21 | = | 3 . 7 |
| Prime factors of 77 | = | 7 . 11 |
| Prime factors of 91 | = | 7 . 13 |
3. Choose the common prime factors with the lowest exponent
Common prime factors: 7
Common prime factors with the lowest exponent: 71
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 = 71 = 7
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