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In terms of Sequence are t1, t2, t3, ....tn, what is value

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In terms of Sequence are t1, t2, t3, ....tn, what is value [#permalink] New post 10 Jan 2009, 22:52
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In terms of Sequence are t1, t2, t3, ....tn, what is value of n?

1) Sum of n terms is 3124
2) Average of n terms is 4
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Re: DS-Sequence [#permalink] New post 11 Jan 2009, 06:56
1. sum of n terms is 3124
It means that t1+...tn=3124=>insuff
2. t1+...tn=4n=> insuff

Combine 1 &2 : 4n=3124 => suff

C is the best answer
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Re: DS-Sequence [#permalink] New post 11 Jan 2009, 16:04
I choose E.

1. n(n+1)/2 = 3124 => solving for n gives -3 or 2. Therefore 2. Sufficient
2. n(n+1)/2n = 4 => solving for n gives 0 or 7. Therefore 7. Sufficient
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Re: DS-Sequence [#permalink] New post 12 Jan 2009, 01:31
ic3ncok3 wrote:
I choose E.

1. n(n+1)/2 = 3124 => solving for n gives -3 or 2. Therefore 2. Sufficient
2. n(n+1)/2n = 4 => solving for n gives 0 or 7. Therefore 7. Sufficient


Not really sure where you're going here. First, if you think each statement is sufficient, you should be choosing D, not E. You also seem to be assuming that the sequence is a sequence of consecutive integers beginning from 1 - that's the only situation where you could use the "sum = n(n+1)/2" formula. You aren't told what kind of sequence this is, so you can't use any formula for the sum here. Finally, I don't understand how you arrived at the solutions -3 and 2 from the equation n(n+1)/2 = 3124.

prosper's solution is correct.
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Re: DS-Sequence   [#permalink] 12 Jan 2009, 01:31
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