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GMATPrep sequence

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Nihit
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GMATPrep sequence [#permalink] New post   13 Jun 2008, 01:21
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 01:41
I think the answer is (E).

(1) is insufficient since it is just a relation between one term and the following (but it gives no clue about the beginning of the sequence)

(2) is insufficient since it justs gives a relation between the 4th and 5th terms (we can't infer anything about the other terms)

(1) and (2) is insufficient too : \(x5=x4/(x4+1)\) and \(x5=x4/2\) means \(x4/2=x4/(x4+1)\) which translates into \(x4(x4-1)=0\) i.e. x4=0 or x4=1

Then we know that either \(x1=0\) or \(x1=8\), but we don't know which to pick unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 01:46
Oski wrote:
I think the answer is (E).

(1) is insufficient since it is just a relation between one term and the following (but it gives no clue about the beginning of the sequence)

(2) is insufficient since it justs gives a relation between the 4th and 5th terms (we can't infer anything about the other terms)

(1) and (2) is insufficient too : \(x5=x4/(x4+1)\) and \(x5=x4/2\) means \(x4/2=x4/(x4+1)\) which translates into \(x4(x4-1)=0\) i.e. x4=0 or x4=1

Then we know that either \(x1=0\) or \(x1=8\), but we don't know which to pick unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"


Its C

X is "positive" number; 0 is neither positive nor negative
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 01:46
Oski wrote:
I think the answer is (E).

(1) is insufficient since it is just a relation between one term and the following (but it gives no clue about the beginning of the sequence)

(2) is insufficient since it justs gives a relation between the 4th and 5th terms (we can't infer anything about the other terms)

(1) and (2) is insufficient too : \(x5=x4/(x4+1)\) and \(x5=x4/2\) means \(x4/2=x4/(x4+1)\) which translates into \(x4(x4-1)=0\) i.e. x4=0 or x4=1

Then we know that either \(x1=0\) or \(x1=8\), but we don't know which to pick unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"



The answer is C, based on your calculation (which is exactly what i did), BUT here is the trap, the question says its a seq of positive integers, and 0 isn't positive, so x1 = 8
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 01:55
buffdaddy wrote:
The answer is C, based on your calculation (which is exactly what i did), BUT here is the trap, the question says its a seq of positive integers, and 0 isn't positive, so x1 = 8

OK, I still have to get used to the english vocabulary in these tests ;).

For me 0 can be called 'positive' and 'negative' at the same time thus my caveat:

Quote:
unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 02:13
Oski wrote:
buffdaddy wrote:
The answer is C, based on your calculation (which is exactly what i did), BUT here is the trap, the question says its a seq of positive integers, and 0 isn't positive, so x1 = 8

OK, I still have to get used to the english vocabulary in these tests ;).

For me 0 can be called 'positive' and 'negative' at the same time thus my caveat:

Quote:
unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"


Hi Oski,

for GMAT purposes 0 is not positive and not negative.
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 02:23
OA is not C . :twisted:
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 03:29
buffdaddy wrote:
Oski wrote:
buffdaddy wrote:
The answer is C, based on your calculation (which is exactly what i did), BUT here is the trap, the question says its a seq of positive integers, and 0 isn't positive, so x1 = 8

OK, I still have to get used to the english vocabulary in these tests ;).

For me 0 can be called 'positive' and 'negative' at the same time thus my caveat:

Quote:
unless we suppose that when they say "positive numbers" they mean "non negative positive numbers"


Hi Oski,

for GMAT purposes 0 is not positive and not negative.

Thanks ! I'm just starting with it ;)
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 08:37
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I believe that it is C. But if C is not OA, therefore I missed something.

1) \(x_i=\frac{x_{i-1}}{2}\) for i>1
Clear insufficient.
64,32,16,8,4,2,1,1/2....
16,8,4,2,1,1/2,1/4,1/8....

2) second condition says us only about relations between \(x_5\) and \(x_4\). insufficient.

1)&2) \(\frac{x_{4}}{2}=\frac{x_4}{x_4+1}\) ---> \(x_4=0\) or \(x_4=1\). 0 is not positive, so \(x_4=1\) and \(x_1=8\)
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Re: GMATPrep sequence [#permalink] New post   13 Jun 2008, 13:54
Yeah seems like C to me as well , What is the OA ?



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Re: GMATPrep sequence [#permalink]
13 Jun 2008, 13:54
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