Data Sufficiency

GMATinsight wrote:What is the standard deviation of set A?

1) Mean of the set A is 10
2) Range of the set A is 0

Target question: What is the standard deviation of set A?

Statement 1: Mean of the set A is 10
There are several sets that satisfy statement 1. Here are two:
Case a: Set A = {10, 10, 10}. The mean = 10. In this case, the standard deviation of set A is 0
Case b: Set A = {0, 10, 20}. The mean = 10. In this case, the standard deviation of set A is NOT 0
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: Range of the set A is 0
If the range is 0, then every value in set A is the same.
In other words, the the standard deviation of set A is 0
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

Cheers,
Brent