Bunuel wrote:

If a is a positive number less than 10, is c greater than the average (arithmetic mean) of a and 10?

(1) c = 3a

(2) On the number line, c is closer to a than it is to 10.

Is c > (a+10)/2 Or Is 2c > (a+10)?

(1) c = 3a, then 2c = 6a. So now the question becomes:

Is 6a > a+10 Or Is 5a > 10 Or Is a > 2?

Since comparison of a with 2 is not given, we cannot answer the question. So

Insufficient.

(2) The nature of average of two numbers is such that it will lie exactly in the middle of the two numbers. So the average of a and 10 will lie exactly in the middle of a and 10 on the number line. But we are given that c is closer to a than to 10, so this means c is lesser than the average of a and 10. Thus this gives us NO as an answer to the question asked. So this is

sufficient.

Hence

B answer