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The nth term (tn) of a certain sequence is defined as tn = t

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Senior Manager
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Joined: 15 Sep 2010
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The nth term (tn) of a certain sequence is defined as tn = t [#permalink]

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24 Nov 2010, 09:50
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88% (01:03) correct 13% (00:11) wrong based on 9 sessions

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The nth term (tn) of a certain sequence is defined as tn = tn-1 + 4. If t1= -7 then t71 =

OA
[Reveal] Spoiler:
273

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Re: nth term of sequence [#permalink]

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24 Nov 2010, 09:59
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shrive555 wrote:
The nth term (tn) of a certain sequence is defined as
tn = tn-1 + 4. If t1= -7 then t71 =

OA=273

Given: $$t_n=1_{n-1}+4$$.

Then: $$t_2=t_1+4$$, $$t_3=t_2+4=t_1+2*4$$, $$t_4=t_3+4=t_1+3*4$$... --> $$t_n=t_1+(n-1)*4$$.

So, $$t_{71}=t_1+70*4=-7+280=273$$.
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Re: nth term of sequence [#permalink]

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24 Nov 2010, 18:51
Here is another way:

Given: T1 = Tn-1 +4 & T1 = -7

Then solve to get the
Direct Formula:
Tn = k*n+x k is the constant change which is 4 in this problem, find x

T1 = k + x
T1: -7 = 4 + x
x = -11

Tn= 4*n -11

Use this formula to find T71:
T71= 4*(71) -11
= 284 - 11
= 283
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Re: nth term of sequence [#permalink]

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24 Nov 2010, 18:59
shrive555 wrote:
The nth term (tn) of a certain sequence is defined as
tn = tn-1 + 4. If t1= -7 then t71 =

OA=273

I see you are working with sequences and series today. The story I wrote in response to your previous question will work perfectly well here too since this is an arithmetic progression too. If you understand it, you will get this question on your own. Go back and read it again and try this question again. If you don't get it, let me know what you don't understand in the theory.
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Re: The nth term (tn) of a certain sequence is defined as tn = t [#permalink]

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05 Oct 2017, 05:46
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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: The nth term (tn) of a certain sequence is defined as tn = t   [#permalink] 05 Oct 2017, 05:46
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