Calculate the Greatest Common Factor or GCF of 20, 60, 80 and 120
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The instructions to find the GCF of 20, 60, 80 and 120 are the next:
1. Decompose all numbers into prime factors
| 20 | 2 |
| 10 | 2 |
| 5 | 5 |
| 1 |
| 60 | 2 |
| 30 | 2 |
| 15 | 3 |
| 5 | 5 |
| 1 |
| 80 | 2 |
| 40 | 2 |
| 20 | 2 |
| 10 | 2 |
| 5 | 5 |
| 1 |
| 120 | 2 |
| 60 | 2 |
| 30 | 2 |
| 15 | 3 |
| 5 | 5 |
| 1 |
2. Write all numbers as the product of its prime factors
| Prime factors of 20 | = | 22 . 5 |
| Prime factors of 60 | = | 22 . 3 . 5 |
| Prime factors of 80 | = | 24 . 5 |
| Prime factors of 120 | = | 23 . 3 . 5 |
3. Choose the common prime factors with the lowest exponent
Common prime factors: 2 , 5
Common prime factors with the lowest exponent: 22, 51
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 = 22. 51 = 20
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