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

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If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post Updated on: 20 May 2018, 12:25
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A
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C
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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.

Originally posted by bigsteel79 on 10 Jan 2009, 22:52.
Last edited by Bunuel on 20 May 2018, 12:25, edited 2 times in total.
Renamed the topic and edited the question.
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 28 Jan 2010, 02:59
2
5
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 is the value  [#permalink]

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New post 11 Jan 2009, 06:56
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1
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: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 11 Jan 2009, 16:04
1
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: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 12 Jan 2009, 01:31
1
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: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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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 is the value  [#permalink]

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New post 06 Jan 2016, 11:58
1
Answer is C

Sum of terms= Average of terms * number of terms
3124 = 4 * number of terms
3124/4 = Number of terms
781= Number of terms
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 26 Jan 2017, 05:59
4
Question Stem: What is n?

From Statement 1:The sum of n terms is 3124
=>t1+t2+....+tn=3124----(1)
We cannot find the value of n by this. So insufficient.

From Statement 2:The average (arithmatic mean) of n terms is 4
=>(t1+t2+....+tn)/n=4------(2)
We cannot find the value of n by this. So insufficient.

Combining (1) and (2) by substituting (1) in (2) we get,
3124/n=4....=>n=781
Hence the answer has to be C
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 24 Jul 2017, 01:42
Hi, sorry for digging this up again, but nowhere in the question stem do they mention that the series is an evenly spaced sequence. I chose E based on that logic. Are we to assume that any sequence is evenly spaced?
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 24 Jul 2017, 01:47
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Vishaljain12 wrote:
Hi, sorry for digging this up again, but nowhere in the question stem do they mention that the series is an evenly spaced sequence. I chose E based on that logic. Are we to assume that any sequence is evenly spaced?


You are right we don't know what kind of sequence we are dealing with but it does not matter because for any kind, (average) = (the sum of the terms)/(the number of the terms). When combining the statements we get 4 = 3124/n, so n = 3124/4.

Hope it's clear.
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 24 Jul 2017, 02:48
bigsteel79 wrote:
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


Given : The terms t1,t2,t3,t4...., tn are in sequence. But we don't know which sequence this is
DS : value of n

Statement 1: t1 + t2 + t3 +t4 +.... + tn = 3124
NOT SUFFICIENT

Statement 2: (t1 + t2 +t3 + t4 +... + tn )/n = 4
-> (t1 + t2 +t3 + t4 +... + tn ) = 4n
NOT SUFFICIENT

Combined : 4n = 3124
SUFFICIENT

Answer C
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 20 Jun 2018, 16:27
1
bigsteel79 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.


The sum of the n terms is 3,124.

Since we don’t know anything about each individual term, we can’t determine the number of terms in the sequence. Statement one alone is not sufficient.

Statement Two Only:

The average of the n terms is 4.

Since we don’t know anything about each individual term, we can’t determine the number of terms in the sequence. Statement one alone is not sufficient.

Statements One and Two Together:

Since sum = quantity x average, we have:

3,124 = n x 4

n = 3,124/4 = 781

Answer: C
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value  [#permalink]

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New post 24 Jun 2018, 21:50
n(n+1)/2 = 3124 => solving for n gives -3 or 2
2. n(n+1)/2n = 4 => solving for n gives 0 or 7

both combine sufficient C
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Re: If the terms of a sequence are t1, t2, t3, ..., tn, what is the value &nbs [#permalink] 24 Jun 2018, 21:50
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