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Re: Sequence of terms MGMAT [#permalink]
15 Feb 2011, 07:35

5

This post received KUDOS

Expert's post

mariyea 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.

I think the ans should be D. But OA is different.

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 --> sequence is: 3, 9, 27, 81, ... so the fourth term is 81. Sufficient.

(2) The second-to-last term is 3^10 --> since we don't know how many terms are there in the sequence then we don't know which term is second-to-last. For example: if it's third term then fourth (and last) will be 3^11, if it's fifth term then the fourth term is 3^9, ... Not sufficient.

Re: Sequence of terms MGMAT [#permalink]
15 Feb 2011, 07:59

Bunuel wrote:

mariyea 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.

I think the ans should be D. But OA is different.

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 --> sequence is: 3, 9, 27, 81, ... so the fourth term is 81. Sufficient.

(2) The second-to-last term is 3^10 --> since we don't know how many terms are there in the sequence then we don't know which term is second-to-last. For example: if it's third term then fourth (and last) will be 3^11, if it's fifth term then the fourth term is 3^9, ... Not sufficient.

Answer: A.

I had to think about that for a bit before I could sincerely agree with you, Bunuel. Thanks!
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Re: Sequence of terms MGMAT [#permalink]
15 Feb 2011, 10:03

Bunuel wrote:

mariyea 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.

I think the ans should be D. But OA is different.

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 --> sequence is: 3, 9, 27, 81, ... so the fourth term is 81. Sufficient.

(2) The second-to-last term is 3^10 --> since we don't know how many terms are there in the sequence then we don't know which term is second-to-last. For example: if it's third term then fourth (and last) will be 3^11, if it's fifth term then the fourth term is 3^9, ... Not sufficient.

Answer: A.

You are truly awesome .. with DS.... i kinda assumed it to be 2nd term when said 2nd to last assuming that there r only 4 terms...thanks bunuel...

Re: In a sequence of terms in which each term is three times the [#permalink]
13 Jan 2012, 15:39

Bunuel wrote:

mariyea 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.

I think the ans should be D. But OA is different.

regarding the second statement. Someone could interpret the second-to-last term as the ratio between the second and the last term.

Since we know that it is an exponential expression dividing the second with the last term should result a fraction smaller than 1. Therefore, someone could assume that the second statement is wrong.

Re: In a sequence of terms in which each term is three times the [#permalink]
16 Jan 2012, 16:24

1

This post received KUDOS

Expert's post

SonyGmat wrote:

Bunuel wrote:

mariyea 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.

I think the ans should be D. But OA is different.

regarding the second statement. Someone could interpret the second-to-last term as the ratio between the second and the last term.

Since we know that it is an exponential expression dividing the second with the last term should result a fraction smaller than 1. Therefore, someone could assume that the second statement is wrong.

is my reasoning valid?

Responding to a pm.

If it were the case it would have been something like "the ratio of second to last term is ..."

Also on the GMAT, two data sufficiency statements always provide TRUE information and these statements never contradict each other. So if on the GMAT your interpretation of the statements leads you to conclude that the statements are impossible/incorrect or contradict each other then the case would be that your interpretation is wrong not the statements.
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