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If the terms of a sequence are t1, t2, t3, . . . , tn, what

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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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C
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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
[Reveal] Spoiler: OA
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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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If the terms of a sequence are t1, t2, t3, . . . , tn, what [#permalink] New post 27 Jan 2010, 20:25
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If the terms of a sequence are t1, t2, t3, . . . , tn, what is the value of n ?

(1) The sum of the n terms is 3,124.

(2) The average (arithmetic mean) of the n terms is 4.
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Re: If the terms of a sequence are t1, t2, t3, . . . , tn, what [#permalink] New post 28 Jan 2010, 02:58
ugimba wrote:
If the terms of a sequence are t1, t2, t3, . . . , tn, what is the value of n ?

(1) The sum of the n terms is 3,124.

(2) The average (arithmetic mean) of the n terms is 4.



If we have a Arithmetic Seq, sum is n/2(2a+(n-1)d)
(1) NOT SUFF as it can be sum of any number of seq with diff n.

(2) AM is 4, For a Arithmetuc Seq, AM is (2a+(n-1)d)/2. NOT SUFF.

(1) and (2) => n*4=3124 => n= 781. SUFF

Answer is C
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Re: If the terms of a sequence are t1, t2, t3, . . . , tn, what [#permalink] New post 28 Jan 2010, 02:59
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Ans should be C


t1+t2+.....tn = 3124

avg = total sum/n =4

=> 3124/n =4
=> n = 3124/4

=> n =781

Both taken together are sufficient to ans this ques...thus C
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Re: If the terms of a sequence are t1, t2, t3, . . . , tn, what [#permalink] New post 10 Aug 2014, 07:54
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Re: If the terms of a sequence are t1, t2, t3, . . . , tn, what   [#permalink] 10 Aug 2014, 07:54
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