MathDB
Math Prize 2010 Problem 4

Source:

November 14, 2010

Problem Statement

Consider the sequence of six real numbers 60, 10, 100, 150, 30, and xx. The average (arithmetic mean) of this sequence is equal to the median of the sequence. What is the sum of all the possible values of xx? (The median of a sequence of six real numbers is the average of the two middle numbers after all the numbers have been arranged in increasing order.)