Question

Which number is NOT a common factor OF 15, 45, AND 90?
A) 3
B) 5
C) 10
D) 15

Answer 1

The answer is is b) 10

Answer 2

none, but 7 is not a common factor of 15,45,and 90

think about it. 

3 x 5=15   <<== that already eliminates it

5 x 3= 15  <<== that also eliminates it

10 x 9= 90 <<== eliminated

15 x 1= 15 <<== so all of them are eliminated as an answer