Is the integer n a multiple of 15?

[ST]

Is the interger n a multiple of 15?

1) n is a multiple of 20.
2) n+6 is a multiple of 3

answer is C

Could anyone explain this?

[2010gmat]

1. In suff -- n is a multiple of 20 .. can be 40, 60 , etc
2. n+ 6 is multiple of 3 ... In suff .. as it can be anything -- 6,9 ,15

taking 1 and 2 together.... n is a multiple of 20 and 3 ---> n has factors 2, 3 and 5 ---> n is a multiple of 15...

---> c
hope it helps u...was easy to solve but difficult to explain :roll: