Answer:
13
Explanation:
You want the greatest common factor (k) that allows you to rewrite 13+65 as k(1 + __).
Distributive property
The distributive property tells you that the expression ...
k(1 +a)
expands to ...
k +ka.
Comparing this to 13 +65, we see k = 13, and a = 65/13 = 5.
The greatest common factor is 13.
The rewritten expression is ...
13 +65 = 13(1 +5)
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Additional comment
As we show here, the fact that you end up with 1+ inside parentheses tells you that the first number (13) is the greatest common factor.