Data Sufficiency

If the average (arithmetic mean) of 9 numbers is 43, what is the standard deviation of them?
1) The smallest number of them is 43
2) The greatest number of them is 43

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This is a recent trend question type. If range=M-m=0, mean=Max, or mean=min, then SD=0.
Condition 1) gives us mean=min, SD=0
Condition 2) also gives us mean=Max, SD=0. Hence, the correct answer is D.
- Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.