Wayxi wrote:
Is the integer n a multiple of 15 ?
1) n is a multiple of 20
2) n + 6 is a multiple of 3
Please explain how to derive the answer to this question. Thanks
Start with statement 1. It is not sufficient because for a number to be a multiple for 15, it should be divisible by both 3 and 5. Clearly, 20 does not have 3 as a factor. Hence, statement 1 is not sufficient.
Statement 2 says that n+6 is a multiple of three. If you break it down, it is basically saying that n is a multiple of 3. But that we don't know whether n is a multiple of 5 or not. Hence, this is not sufficient.
If you combine both 1 and 2, you can conclude that n has both 5 (from statement 1)and 3 (from statement 2) as factors. Hence, C is the answer.