In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 : DS Archive
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# In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1

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In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]

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10 Jul 2008, 22:49
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In the sequence of nonzero numbers t1, t2, t3, …, tn, …, tn+1 = tn / 2 for all positive integers
n. What is the value of t5?
(1) t3 = 1/4
(2) t1 - t5 = 15/16
Director
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10 Jul 2008, 22:53
goalsnr wrote:
In the sequence of nonzero numbers t1, t2, t3, …, tn, …, tn+1 = tn / 2 for all positive integers
n. What is the value of t5?
(1) t3 = 1/4
(2) t1 - t5 = 15/16

D

its a GP : a, ar, ar^2, ar^3 ....

As per question we know r = t(n+1) / tn = 1/2

question what is ar^4

we can calcutale a from both statement 1 and 2
SVP
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11 Jul 2008, 04:50
i agree with D

from stat 1 , you can calculate t5 pretty quickly. suff

from stat 2, you can rewrite t5 in terms of t1, figure out t1, and subsequently find out t5 ... ie t5=t4/2=t3/4=t2/8=t1/16
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11 Jul 2008, 11:46
goalsnr wrote:
In the sequence of nonzero numbers t1, t2, t3, …, tn, …, tn+1 = tn / 2 for all positive integers
n. What is the value of t5?
(1) t3 = 1/4
(2) t1 - t5 = 15/16

I have a question... where does this question come from?
The problem already stated the condition is for all positive integers
Notice how the conditions are given, with both being fractions.
I think the question needs to be rephrase to all positive numbers....
Then, the answer should be D..
Otherwise E? (I don't know what to make of it)
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Senior Manager
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11 Jul 2008, 17:53
You are given tn+1 = tn/2
Therefore the first term will be t, the second term t/2, the third term t/4
s1. tells you that t/4 = 1/4 hence t =1

s2. t1 - t5 = 15/16
1 - t5 = 15/16
Therefore t5 = 1/16

Director
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11 Jul 2008, 18:30
fatb wrote:
goalsnr wrote:
In the sequence of nonzero numbers t1, t2, t3, …, tn, …, tn+1 = tn / 2 for all positive integers n. What is the value of t5?
(1) t3 = 1/4
(2) t1 - t5 = 15/16

I have a question... where does this question come from?
The problem already stated the condition is for all positive integers
Notice how the conditions are given, with both being fractions.
I think the question needs to be rephrase to all positive numbers....
Then, the answer should be D..
Otherwise E? (I don't know what to make of it)

the question is refering n as a positive integer, not the terms of the sequence.
Re: DS-seq   [#permalink] 11 Jul 2008, 18:30
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