Hi Vincen,

When given a group of numbers, the 'range' is the difference between the largest number and the smallest number. Here, we're given a set of numbers that includes a variable:

{2, 8, 13, 15, X}

The value of X could be smaller than 2, greater than 15 or something 'in between.' We're told that the range of this group is 2X though, so we have to find a value of X that would lead to that specific range.

Using the 4 numbers that we're given, we know that the range is at least 15-2 = 13 (and it could be greater depending on the value of X). Focusing on that minimum range though, if we set 2X = 13, then X would be 6.5; that answer IS among the five answer choices, so we can stop working.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich