Hi sachin_yadav,
What is the source of this question? I ask because the 'design' of this question is incorrect (the two Facts CANNOT BOTH be sufficient while giving different answers).
We're told that the average of a group of numbers is 5. We're asked for the Standard Deviation of the group.
1) None of the numbers are greater than this Average
The ONLY way that this can occur is if ALL of the numbers in the set are the SAME number. Thus, while we don't know how many numbers are in the set, we do know that they are all 5s. By extension, the SD = 0
Fact 1 is SUFFICIENT.
2) The Standard deviation is 5 when value of each of the given number is increased by 7
This Fact doesn't tell us what the numbers are, BUT if we increase EACH number by 7, then the Stand Deviation would still the SAME. By extension, the SD = 5
Fact 2 is SUFFICIENT.
This would make the answer D, but the GMAT does NOT create its DS questions in this way. The SD CANNOT be 0 and 5.
GMAT assassins aren't born, they're made,
Rich
