What is the greatest common factor of 42a5b3?

To find the greatest common factor of 42a^5b^3, we need to factorize the expression into its prime factors.

42 can be factored as 2 * 3 * 7, a^5 can be factored as a * a * a * a * a, b^3 can be factored as b * b * b.

The greatest common factor of 42a^5b^3 would be the product of the common factors between the multiple terms, which in this case would be 1 (as there are no common factors between all the terms - 42, a^5 and b^3).

Therefore, the greatest common factor of 42a^5b^3 is 1.