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The second-to-last term

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The second-to-last term

by diaca » Wed Feb 02, 2011 4:07 pm
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.


A

Does somebody know what is the meaning of the second statement?, what can I get from it.?

Thank
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by cyrwr1 » Wed Feb 02, 2011 4:45 pm
A is my answer.

1) Given 1st term: 1
2nd: 3
3rd:3*3
4th: 3*3*3

2) this tells that with n numbers in the sequence, the (n-1)th term is 10 and this tells us nothing as 'n' can equal anything.
The number of terms is not given so you do not know if there are just 5 terms for the answer.
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by Rahul@gurome » Wed Feb 02, 2011 7:02 pm
diaca 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.


A

Does somebody know what is the meaning of the second statement?, what can I get from it.?

Thank
Solution:
Consider first (1) alone.
The first term is 3.
So the sequence is of the form 3, 9, 27, 81...
This means that fourth term is 81.
Or (1) alone is sufficient.
Next, consider (2) alone.
It means that if the term just before the last term in the sequence is 3^10.
This is definitely not enough to tell us the fourth term of the sequence since we will
need to know either the first term or the number of terms in the sequence.
So, (2) alone is not sufficient.

The correct answer is (A).
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