Data Sufficiency

sachin_yadav wrote:If two elements are dropped from set X {-10, -8, 0, 6, 7}, what will be the percentage change in its mean?

(1) The median of the set will remain the same
(2) The range of the set will decrease by 3

Target question: What will be the percentage change in the set's mean?

Given: Two elements are dropped from set X {-10, -8, 0, 6, 7}
The CURRENT mean of set X is -1

Statement 1: The median of the set will remain the same
The current median of set x is 0. There are several ways to remove two elements and have the median REMAIN at 0. Here are two possible cases:
Case a: remove -10 and 7, to get {-8, 0, 6}. Here the median is still 0. In this case , the mean changes from -1 to -2/3, which represents a 33 1/3 percent decrease.
Case b: remove -10 and 6, to get {-8, 0, 7}. Here the median is still 0. In this case , the mean changes from -1 to -1/3, which represents a 66 2/3 percent decrease.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: The range of the set will decrease by 3
The ONLY way to remove two elements have have the range decrease by 3 is to remove -10 and 7 and get {-8, 0, 6}.
When we do this, the mean changes from -1 to -2/3, which represents a 33 1/3 percent decrease.
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = B

Cheers,
Brent