Problem Solving

Hi LulaBrazilia,

Sometimes the easiest way to answer a Quant question is to "brute force" it - just do the work on the pad and get the answer as quickly as possible.

Here, we're asked to compare the AVERAGE of the first 10 positive multiples of 5 to the MEDIAN of the first 10 positive multiples of 5.

The numbers: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50

To get the average, rather than add these numbers in order, we can "bunch" them.
5+50 = 55
10+45 = 55
etc.
So we have 5 sets of 55 = 275

Average = 275/10 = 27.5

The median in a set of 10 terms is the average of the 5th and 6th values. The average of 25 and 30 is...

55/2 = 27.5

So, the average - the median = 27.5 - 27.5 = 0

Final Answer: B

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

LulaBrazilia wrote: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