Problem of the Week 1160
Many Pairs Dividing a Sum
Given four distinct positive integers a, b, c, d, let S be their sum.
Let x1, x2, x3, x4, x5, x6 be the six possible sums of the given four, two at a time.
Find an example where the number of the six x's that divide S is as large as possible.
Source: Bart de Smit, IMO 2011.
© Copyright 2012 Stan Wagon. Reproduced with permission.