Question 848457
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Hi,
how many students {{{ highlight_green(n)}}}are there in a group 
n(n-1) = 90    (each in the group giving remaining group members a gift)
 n^2 - n - 90 = 0
(n-10)(n+9) = 0   (Tossing out the negative solution for unit measure)  
  n = 10 in the group