Five numbers added together in pairs produce: 0, 2, 4, 4, 6, 8, 9, 11, 13, 15 What are the five numbers?
Weekly Problem 16 - 2012
Weekly Problem 47 - 2013
If p is a positive integer and q is a negative integer, which of the following is the greatest? A. $p-q$ B. $q-p$ C. $p+q$ D. $-p-q$ E. More information needed
If you liked this question, here is an NRICH task which challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.