If m is the average (arithmetic mean) of the first 10 positi

[BTGmoderatorAT]

If m is the average (arithmetic mean) of the first 10 positive multiples of 5 and if M is the median of the first 10 positive multiples of 5, what is the value of M - m ?

(A) -5
(B) 0
(C) 5
(D) 25
(E) 27.5

I'm confused how to set up the formulas here. Can any experts help?

[GMATGuruNY]

If m is the average (arithmetic mean) of the first 10 positive multiples of 5 and if M is the median of the first 10 positive multiples of 5, what is the value of M - m ?

(A) -5
(B) 0
(C) 5
(D) 25
(E) 27.5

For any EVENLY SPACED SET, mean = median.
The first 10 positive multiples of 5 constitute an evenly spaced set.
Thus, mean = median, implying that M=m and that M-m = 0.

The correct answer is B.

[Scott@TargetTestPrep]

If m is the average (arithmetic mean) of the first 10 positive multiples of 5 and if M is the median of the first 10 positive multiples of 5, what is the value of M - m ?

(A) -5
(B) 0
(C) 5
(D) 25
(E) 27.5

To answer this question we can use the following rule:

When we have an evenly spaced set of numbers, the mean and the median are equal. Recall that in an evenly spaced set of numbers there is a common difference between consecutive terms in the set. For example, consecutive integers, consecutive odd integers, consecutive even integers, and consecutive multiples of any given number are all examples of evenly spaced sets.

Thus the answer is 0.

Answer: B