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sum of the integer from 1 to 2n

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by vishubn » Sun Nov 16, 2008 5:13 am
n=10

1- 2n is 1-20

20(21)/2

121

sub n=10


A)10*11=false
B)5*21 -false
C)10*21-true
D)20*11-false
E)20*21-Fa;lse

OA C

confirm please

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KILL !! DIE !! or BEAT my FEAR !!! de@D END!!
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by mals24 » Sun Nov 16, 2008 5:13 am
IMO C

Just put 2n in place of n and simplify.

2n(2n+1)/2 = n(2n+1)
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by cramya » Sun Nov 16, 2008 12:55 pm
Mals24 solution is good.

If we have problems we can pick numbers

lets say 1,2,3 here n=3 sum is 6

2n= 6 i.e 6 numbers 1,2,3,4,5,6 Sum = 21

Only choice that will work is C) N(2N+1)

3(6+1) = 21

Done C)
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