Question 846969: In a group of children, each child gives one gift to other. If total numbers of gift are 90, then find the number of children in the group.
Answer by josgarithmetic(39617)   (Show Source):
You can put this solution on YOUR website! This would be just like the "hand-shake" problem. You would want to be able to make a polygon so that you can show 90 individual connections among all vertices. Start with a triangle; it has 3 connections. Next use a square (four sides); it will have 4 connections. Next, use a pentagon; it has 7 connections. Continue on this way...
Look at the wikipedia article, http://en.wikipedia.org/wiki/Handshake_problem
See the section about Triangular Numbers. The given 90 gifts in your exercise would most closely correspond to 14 students.
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