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In the arithmetic sequence  [#permalink]

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Question Stats: 63% (01:34) correct 37% (00:30) wrong based on 19 sessions

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In the arithmetic sequence $$t_1, t_2, t_3, . . . , t_n$$ and $$t_1 = 23$$ and $$t_n = t_{n - 1} - 3$$ for each $$n > 1$$.
What is the value of n when $$t_n = -4$$?

(A) -1
(B) 7
(C) 10
(D) 14
(E) 20

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Tashin

Originally posted by Tashin Azad on 29 Dec 2018, 20:06.
Last edited by Gladiator59 on 30 Dec 2018, 08:46, edited 1 time in total.
Formatted the post and topic name.
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Re: In the arithmetic sequence  [#permalink]

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t1=23
tn=tn-1 -3
Thus, we can see that this is an arithematic progression with -3 as the gap between 2 successive elements.
Thus, when tn= -4, d=-3 and t1=23
tn= t1+ (n-1)d
-4=23+ (n-1)*-3
this implies, n=10
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Re: In the arithmetic sequence  [#permalink]

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1
$$t_1,t_2,......t_n$$

$$t_1 = 23$$

$$t_n = t_{n-1}-3$$

first term = 23, common difference (d) = -3

$$t_n = -4$$

$$n^{th} term = a+(n-1)d$$

$$23+(n-1)(-3) = -4$$

$$23-3n+3 = -4$$

$$30 = 3n$$

$$n = 10$$

OPTION: C
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Re: In the arithmetic sequence  [#permalink]

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In the arithmetic sequence t1, t2, t3, . . . , tn, . . . , t1 = 23 and tn = tn - 1 - 3 for each n > 1.
What is the value of n when tn = -4 ?

(A) - 1
(B) 7
(C) 10
(D) 14
(E) 20

Gladiator59, Bunuel I think this question needs to be formatted so $$t_n = t_{n-1}-3$$ Senior PS Moderator D
Status: It always seems impossible until it's done.
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GMAT 1: 740 Q50 V40 GMAT 2: 770 Q51 V42 Re: In the arithmetic sequence  [#permalink]

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1
Thanks for pointing out. Edited the post.

Regards,

dave13 wrote:

Gladiator59, Bunuel I think this question needs to be formatted so $$t_n = t_{n-1}-3$$ _________________
Regards,

“Do. Or do not. There is no try.” - Yoda (The Empire Strikes Back)
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GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: In the arithmetic sequence  [#permalink]

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Hi All,

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

GMAT assassins aren't born, they're made,
Rich
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Re: In the arithmetic sequence  [#permalink]

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In the arithmetic sequence $$t_1, t_2, t_3, . . . , t_n$$ and $$t_1 = 23$$ and $$t_n = t_{n - 1} - 3$$ for each $$n > 1$$.
What is the value of n when $$t_n = -4$$?

(A) -1
(B) 7
(C) 10
(D) 14
(E) 20

Discussed here: https://gmatclub.com/forum/in-the-arith ... 29374.html

TOPIC US LOCKED AND ARCHIVED.
_________________ Re: In the arithmetic sequence   [#permalink] 31 Dec 2018, 01:12
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