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![[Post New]](/templates/default/images/icon_minipost_new.gif) 29 Mar 2008 20:58:47 IST
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take different cases
if y=9 then x is bet 1-8 and z bet 0-8
therefore no of ways of choosing x and z is 9(9-1)
for y=r
no of ways is r(r-1)
hence tot no of ways is= [1] [ 9] [r(r-1)]
=[1] [ 9] [r2-r]
= n(n+1)(2n+1)/6 - n(n+1)/2
=285-45=240
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