Using Euclid's algorithm, divide 76 by 24. The result is 3 r 4. Now, divide 24 by the remainder. That result is 6 r 0. Since the remainder is zero, the divisor (4) is the greatest common factor of 76 and 24.
The GCF of 76 and 24 is 4.
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Another way to look at it is to factor the two numbers and see what factors they have in common.
76 = 4·19
24 = 4·6
since 6 an 19 have no common factors, 4 is the greatest common factor of 76 and 24.