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what is value of n?

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deepak.yakkundi
 Post subject: what is value of n?
 Post Posted: Thu Aug 26, 2010 7:23 am 
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Students


Posts: 3
Q. If the terms of a sequence are t1, t2, t3......tn what is the value of n?

1. The sum of n terms is 3124

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


The OA is C.

If the sequence is AP, then ans is C..
but the sequence can be AP or GP or HP...

so why did we assume the sequence to be AP..

Can somebody explain?
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gokul_nair1984
 Post subject: Re: what is value of n?
 Post Posted: Thu Aug 26, 2010 7:58 am 
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Students


Posts: 170
Why do you want to complicate things by bothering so much about whether the terms are in HP GP or AP?

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

Even if the GMAT questions you on GP/HP or even AP for that matter, the question will always explain the pattern of that function.In short you do not need to memorise the formulae for GP/HP. Memorising the AP formula might help save some time, but even if you don't you can easily solve any problems regarding the same.
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RonPurewal
 Post subject: Re: what is value of n?
 Post Posted: Thu Sep 16, 2010 7:00 am 
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ManhattanGMAT Staff


Posts: 7146
please search the forum; for a question with as many words as this one, it should be extremely easy to find the question on existing threads.

here's one:
f-the-terms-of-a-sequence-t1-t2-tn-what-is-t2034.html
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