Question 846972
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Hi,
each child gives one gift to the other 
total gifts are 90
{{{n(n-1) = 90}}}
  n(n-1) = 90
 n^2 - n = 90
 n^2 - n - 90 = 0     (Tossing out the negative solution for unit measure)
(n-10)(n+9) = 0 ,   n = 10 children in the group