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a sequence of terms

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a sequence of terms

by sanju09 » Wed Mar 02, 2011 6:14 am
In a sequence of terms in which each term is three times the previous term, what is the fourth term?

(1) The first term is 3.

(2) The second to last term is 310.
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by Night reader » Wed Mar 02, 2011 7:04 am
given set a(i=1 -> n), a(n)=3*a(n-1), find a(n=4) or a(4)-?
st(1) a(1)=3, a(4) = 3^4 Sufficient
st(2) a(n-3)=3^10, Not sufficient, as we don't know the last term is what (it could be anything ...)

IOM A

please don't forget to recheck the notation for your posted question next time

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sanju09 wrote:In a sequence of terms in which each term is three times the previous term, what is the fourth term?

(1) The first term is 3.

(2) The second to last term is 310.
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by sanju09 » Sat Apr 30, 2011 2:33 am
Night reader wrote:given set a(i=1 -> n), a(n)=3*a(n-1), find a(n=4) or a(4)-?
st(1) a(1)=3, a(4) = 3^4 Sufficient
st(2) a(n-3)=3^10, Not sufficient, as we don't know the last term is what (it could be anything ...)

IOM A

please don't forget to recheck the notation for your posted question next time

Thanks
sanju09 wrote:In a sequence of terms in which each term is three times the previous term, what is the fourth term?

(1) The first term is 3.

(2) The second to last term is 310.
and what do you mean by that :) ?
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by sourabh33 » Sun May 01, 2011 6:03 pm
Hi Sanju

I have a small doubt here. As per the general rules of DS in GMAT, both the answers should not be contradictory and not lead to different possible solutions.

If we try to solve the question above, we may never get a common term (either 3 or 310) as mentioned in the options.

Option 1 -> 3__9__27__81__243__729__2187__so on

Option 2 -> __310.00__103.33__34.44__11.48__3.83__1.28

Help!

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by champmag » Sun May 01, 2011 11:17 pm
It is obvious that the 4th term can be easily found since the 3rd term is given.

A--sufficient to answer the question.

Since the total number of terms in the series are not specified, we dont know that the second last term is actually which term in the series ( whether its 1st, 2nd, 3rd , 4th..). So statement B is not sufiicient to answer the question. Thus A.
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by Jeff@TargetTestPrep » Fri Jan 05, 2018 9:18 am
sanju09 wrote:In a sequence of terms in which each term is three times the previous term, what is the fourth term?

(1) The first term is 3.

(2) The second to last term is 3^10.
Statement One Alone:

The first term is 3.

Our terms are as follows:

3, 9, 27, 81...

So, the fourth term is 81. Statement one alone is sufficient to answer the question.

Statement Two Alone:

The second-to-last term is 3^10.

Since we do not know the number of terms in the set, statement two alone is not sufficient to answer the question.

For example, if there are 4 terms in the set, the fourth term is 3^11. However, if there are 5 terms in the set, the fourth term is 3^10.

Answer: A

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