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# In the sequence of positive numbers X1, X2, X3, ..., what is

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Director
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In the sequence of positive numbers X1, X2, X3, ..., what is [#permalink]  14 May 2006, 04:20
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62% (01:30) correct 37% (00:54) wrong based on 8 sessions
In the sequence of positive numbers X1, X2, X3, ..., what is the value of X1?

1) X(i) = X(i-1)/2
2) X(5) = X(4)/X(4)+1
VP
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Re: DS: Sequence [#permalink]  14 May 2006, 06:49
M8 wrote:
In the sequence of positive numbers X1, X2, X3, ..., what is the value of X1?

1) X(i) = X(i-1)/2
2) X(5) = X(4)/X(4)+1

do you mean X(5) = X(4)/X(4)+1 ......... as .......... X(5) = [X(4)/X(4)] + 1
or as X(5) = X(4)/[X(4)+1] ?
Manager
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Re: DS: Sequence [#permalink]  14 May 2006, 09:57
M8 wrote:
In the sequence of positive numbers X1, X2, X3, ..., what is the value of X1?

1) X(i) = X(i-1)/2
2) X(5) = X(4)/X(4)+1

1) tells us nothing of the values of the terms
2) tells us nothing of the sequence

together:

from 1: Each term is half of the preceeding term.
from 2: the only way for this stmt to be true and to follow the seqyence is if x(4) = 1. Therefore, x(1) = 8.

C
Director
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In the sequence of positive numbers X1, X2, X3, ..., what is the value of X1?

1) X(i) = X(i-1)/2
2) X(5) = X(4)/X(4)+1

From (1), X(1) = x(0)/2
Not Sufficient

From (2), X(1) = X(0)/{X(0) + 1}
Not Sufficient.

Taking both together, lets assume X(0) = a
Thus a/2 = a/(a+1)

Solving for a yields a=1

Hence C

What is OA?
Manager
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Re: DS: Sequence [#permalink]  14 May 2006, 10:25
M8 wrote:
In the sequence of positive numbers X1, X2, X3, ..., what is the value of X1?

1) X(i) = X(i-1)/2
2) X(5) = X(4)/X(4)+1

hm..interesting..

step1) from2), x(5)=2 cuz, X(4)/x(4) = 1
step2) from1) x(5)=x(4)/2 =2 so x(4)=4

... thus, C
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Director
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Re: DS: Sequence [#permalink]  14 May 2006, 11:11
Professor wrote:
do you mean X(5) = X(4)/X(4)+1 ......... as .......... X(5) = [X(4)/X(4)] + 1
or as X(5) = X(4)/[X(4)+1] ?

Sorry Prof, of course X(4)/[X(4)+1]. I do not know how to depict small digits in the sequence in this forum so I just depicted them in parentheses.
Re: DS: Sequence   [#permalink] 14 May 2006, 11:11
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