Calculate the Greatest Common Factor or GCF of 18, 42, 60 and 78
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The instructions to find the GCF of 18, 42, 60 and 78 are the next:
1. Decompose all numbers into prime factors
| 18 | 2 |
| 9 | 3 |
| 3 | 3 |
| 1 |
| 42 | 2 |
| 21 | 3 |
| 7 | 7 |
| 1 |
| 60 | 2 |
| 30 | 2 |
| 15 | 3 |
| 5 | 5 |
| 1 |
| 78 | 2 |
| 39 | 3 |
| 13 | 13 |
| 1 |
2. Write all numbers as the product of its prime factors
| Prime factors of 18 | = | 2 . 32 |
| Prime factors of 42 | = | 2 . 3 . 7 |
| Prime factors of 60 | = | 22 . 3 . 5 |
| Prime factors of 78 | = | 2 . 3 . 13 |
3. Choose the common prime factors with the lowest exponent
Common prime factors: 2 , 3
Common prime factors with the lowest exponent: 21, 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 = 21. 31 = 6
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