Gmat09_5ALL wrote:If the average (arithmetic mean) of 5 different numbers is 12, what is the median of the 5 numbers?
(1) The median of the 5 numbers is equal to 1/3 of the sum of the 4 numbers other than the median.
(2) The sum of the 4 numbers other than the median is equal to 45.

Nice question.
To answer a lot of questions involving the arithmetic mean, we need to know that "If m is the mean of n numbers, then the sum of the numbers is nm"

So, if the mean of 5 number is 12, then the sum of all 5 numbers must be 60 (5x12)

(1) Let m equal the median
60-m is the sum of the 4 numbers other than the median
We now get the equation (60-m)/3 = m
We can solve this equation for m to get m=15
SUFFICIENT

(2) If the sum of all 5 numbers is 60, we know that the median = 60-45
SUFFICIENT

Answer: D