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The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?

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Joined: 07 Sep 2019
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The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?  [#permalink]

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New post 26 Nov 2019, 13:52
Hi there, can someone please help guide me on how to answer this question?
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Re: The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?  [#permalink]

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New post 26 Nov 2019, 14:51
Hi kevinkhan,

When posting subject-specific questions, you should make sure to post them in the appropriate sub-forum. For example, the Problem Solving forum can be found here:

https://gmatclub.com/forum/problem-solving-ps-140/

You should also make sure to post the ENTIRE prompt. The text of the full prompt includes the following 5 answers:

The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?

A. -1
B. 7
C. 10
D. 14
E. 20

There's a full discussion of this prompt here: https://gmatclub.com/forum/in-the-arith ... 29374.html

Questions that use "sequence notation" are relatively rare on Test Day (you'll probably see just 1), but the math behind the sequence is usually some fairly simple arithmetic (add, subtract, multiply, divide).

Here, we're given the first term in the sequence (23) and we're told that each term thereafter is 3 LESS than the preceding term. Once you understand how the sequence "works", in many cases, it's really easy to just "map out" the sequence. We're asked which term in the sequence equals -4.....

1st = 23
2nd = 20
3rd = 17
4th = 14
5th = 11
6th = 8
7th = 5
8th = 2
9th = -1
10th = -4

Thus we know that the answer is 10 (Answer C).

GMAT assassins aren't born, they're made,
Rich
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Contact Rich at: Rich.C@empowergmat.com
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Re: The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?   [#permalink] 26 Nov 2019, 14:51
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The sequence t1, t2, t3...tn, t1=23 and tn=(tn-1)-3, what is tn=-4?

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