The answer is 1 because 7 is a Prime number which means that it's only factors are 1 and itself which is 7.
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That is just a rubbish answer. The key is not whether one of the numbers is prime but whether the numbers in the set are co-prime.
GCF(7, 42) = 7.
Although 7 is a prime and divides itself, it also divides 42.
Since 7 is a factor of 42, it is automatically the GCF.
The GCF of 42 and 35 is 7.factors of 42: 2,6,7factors of 35: 5,7
The GCF of 7, 42, and 70 is 7.The GCF is 7.
The GCF is 7.
The GCF is 7.
The GCF is 7.
The GCF is 7.
GCF of 42 and 112 and 105 is 7.
The GCF is 7.
The GCF is 7.
The GCF is 7.
The GCF is 7.