Official Guide Explanation:
Problem Solving #201

Background

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Solution and Metadata

Question: 201
Page: 181
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Properties of Integers > Factors and Multiples
Category 2: Arithmetic > Descriptive Statistics > Average

Explanation: Any time you are working with a series of consecutive integers or consecutive multiples of an integer--basically, any set of numbers that are equally spaced--recognize that the median and mean of that group is the same. If that isn't intuitive, try it with a few small groups to see it work. In this case, M is the median of a set, and m is the mean of that same set. Since the set consists of consecutive multiples of 5, the median and mean are equal, so M - m = 0, choice (B).

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