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by bblast » Thu Aug 11, 2011 7:21 am
A certain computer has 2000 megabytes of memory. Memory is considered "free" unless it is being used to run either the programs or the operating system, in which case it is called "in use." Are more than 500 megabytes "free"?

1>The total memory in use is 5 times the memory being used to run the operating system.
2>The amount of memory being used to run the programs is less than the amount of memory that is free.


C
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by gmatboost » Thu Aug 11, 2011 7:54 am
Free = F
Operating System = S
Programs = P

F + P + S = 2000
Is F > 500?

1. (P + S) = 5*S
P = 4S
F could be more or less than 500. Insufficient.

2. P < F
F could be more or less than 500. Insufficient.

Combined:
We can easily come up with an example when [spoiler]F > 500[/spoiler]. For example, [spoiler]F = 2000, P = 0, S = 0[/spoiler]. Or many other options.

The challenge is to see if we can come up with one where [spoiler]F <=500[/spoiler].
We should test this by trying [spoiler]F = 500[/spoiler]. The biggest P could be then is about 500 also. This leaves S to be 125. So, the total is not nearly 2000. F has to be bigger than 500.

Another way of reasoning is that since F > P = 4S, F is the biggest of the 3, so it must take up at least 1/3 of the 2000, which is bigger than 500.
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by bblast » Thu Aug 11, 2011 8:22 am
gmatboost wrote: Another way of reasoning is that since F > P = 4S, F is the biggest of the 3, so it must take up at least 1/3 of the 2000, which is bigger than 500.
awesome, Greg.
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by GmatKiss » Thu Aug 11, 2011 8:23 am
IMO:E
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by GmatKiss » Thu Aug 11, 2011 8:36 am
Hi GB,

Another way of reasoning is that since F > P = 4S, F is the biggest of the 3, so it must take up at least 1/3 of the 2000, which is bigger than 500

How can we reason so,
It is given in (2) that, P < F

Please help me out, if am wrong!
Last edited by GmatKiss on Thu Aug 11, 2011 8:48 am, edited 1 time in total.
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by gmatboost » Thu Aug 11, 2011 8:37 am
F > P is the same as P < F
I just switched the order.
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by GmatKiss » Thu Aug 11, 2011 8:47 am
OMG!! thanks boost, for being so kind :)
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by GMATGuruNY » Thu Aug 11, 2011 9:24 am
bblast wrote:A certain computer has 2000 megabytes of memory. Memory is considered "free" unless it is being used to run either the programs or the operating system, in which case it is called "in use." Are more than 500 megabytes "free"?

1>The total memory in use is 5 times the memory being used to run the operating system.
2>The amount of memory being used to run the programs is less than the amount of memory that is free.


C
Let F = free, P = programs, S = system.

Given that F+P+S = 2000, is F > 500?

Statement 1: P+S = 5S.
P = 4S
Thus, P > S.
No way to determine whether F > 500.

Statement 2: F > P.
No way to determine whether F > 500.

Statements 1 and 2 combined:
Since P > S and F > P:
F > P > S.
If F = 500, then P<500 and S<500, and F+P+S < 1500.
Thus, to satisfy the condition that F+P+S = 2000, F > 500.
Sufficient.

The correct answer is C.
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