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Computer - free memory - in use

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bhumika.k.shah: Legendary Member; Posts: 941; Joined: Sun Dec 27, 2009 12:28 amFollowed by: 1 member; Thanked: 20 times

by bhumika.k.shah » Thu Apr 01, 2010 8:38 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"?

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

Source : Knewton CAT

I wanna know the different approaches and the difficulty level of this Q

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Source: Beat The GMAT — Data Sufficiency | Thu Apr 01, 2010 8:38 am

eaakbari: Master | Next Rank: 500 Posts; Posts: 435; Joined: Mon Mar 15, 2010 6:15 amFollowed by: 1 member; Thanked: 32 times

by eaakbari » Thu Apr 01, 2010 9:10 am

IMO C

Last edited by eaakbari on Thu Apr 01, 2010 11:00 am, edited 1 time in total.

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neoreaves: Master | Next Rank: 500 Posts; Posts: 208; Joined: Sun Sep 28, 2008 12:30 pm; Thanked: 22 times

by neoreaves » Thu Apr 01, 2010 9:17 am

IMO C

What we need to know is if F > 500 MB
T = 2000 MB
F = free mem)
T = F + U (free + used)
U = a + b ( a = operating system , b = program)

1) U = 5a = a + b --> b = 4a --> Insufficient as we dont know anything about F

2) b < F --> Insufficient

C) b = 4a thus 4a < F

Now we only need to know if F > 500 or not

lets say F = 500 then U = 1500 = 4a + a = 5a --> a = 300 and 4a = 1200 ...This is not possible because F is greater than b

Thus the only way this will be true is if F > 500

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Fiver: Master | Next Rank: 500 Posts; Posts: 114; Joined: Mon Sep 22, 2008 3:51 am; Thanked: 8 times; GMAT Score:680

by Fiver » Fri Apr 02, 2010 6:41 am

This problem is similar to the labor and material DS in one of the G-prep tests and is certainly at a 49+ level.

Using both stmts.

Assume:
x - memory to run os
4x - memory to run programs
f - free memory

Given that: 4x+x+f = 2000

with st2] we know that 4x>f and hence f/4>x
Hence 2f+f/4 > 2000

hence f>889

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Fri Apr 02, 2010 10:48 am

bhumika.k.shah 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"?

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

Hi! Thanks for always providing the source - that's very useful info. However, there's no need to hide the source by a spoiler tag. What most people use the spoiler tag for is the answer and/or explanation.

To the question:

Step 1 of the Kaplan Method for DS: Analyze the Stem

We see that there are 3 different possibilities for memory:

-free
-used by the OS
-used by programs

We know that there are 2000MB total.

Q: Is free > 500MB?

We think: we need info about the used memory.

Step 2 of the Kaplan Method for DS: Evaluate the Statements

1) gives us a ratio of OS:program, but no actual numbers: insufficient, eliminate A and C.

2) says nothing about the amount of memory used by the OS and doesn't give us enough info about free/program memory to answer the question: insufficient, eliminate B.

Since neither statement was sufficient alone, we have to combine them.

From 1, we know that programs > OS.

From 2, we know that free > programs.

Combined, we know that:

free > programs > OS.

Since free is the biggest piece, it must account for more than 1/3 of the total memory (if all 3 were equal, they'd be 1/3 each). Since 1/3(2000) > 500, there's definitely more than 500MB of free memory: together sufficient, choose C.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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