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China Western Mathematical Olympiad 2015 ,Problem 1

Source: China Yinchuan Aug 16, 2015

August 17, 2015
inequalitiesalgebra

Problem Statement

Let the integer n2n \ge 2 , and x1,x2,,xnx_1,x_2,\cdots,x_n be real numbers such that k=1nxk\sum_{k=1}^nx_k be integer . dk=minmZxkmd_k=\underset{m\in {Z}}{\min}\left|x_k-m\right| , 1kn1\leq k\leq n .Find the maximum value of k=1ndk\sum_{k=1}^nd_k.