Bea's CDs

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16206; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Thu Jan 29, 2009 2:21 pm

Bea owns how many more CDs than Al owns?
(1) If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns.

(2) If Bea gives 1 CD to Al, and Al purchases 4 additional CDs, then Al and Bea will have an equal number of CDs.

Please note that this is not an official GMAT question; it’s my attempt to create difficult (650+ level) GMAT-style questions for this forum.

Last edited by Brent@GMATPrepNow on Thu Jan 29, 2009 6:49 pm, edited 1 time in total.

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Source: Beat The GMAT — Data Sufficiency | Thu Jan 29, 2009 2:21 pm

dmateer25: Community Manager; Posts: 1049; Joined: Sun Apr 06, 2008 5:15 pmFollowed by: 27 members; Location: Pittsburgh, PA; Thanked: 113 times; GMAT Score:710

by dmateer25 » Thu Jan 29, 2009 5:57 pm

Brent,

Is statement one supposed to be: If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns?

If so, I will go with B.

(2) If Bea gives 1 CD to Al, and Al purchases 4 additional CDs, then Al and Bea will have an equal number of CDs.

B = Bea
A = Al

B-1 = A + 1 + 4
B = A + 6

Bea owns 6 more cd's than al

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16206; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Thu Jan 29, 2009 6:49 pm

Is statement one supposed to be: If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns?

Oops. Yes, you're exactly right, dmateer25. Right about the wording (which I have now changed) and right about the answer (B).

Here's my full solution as well:

Let A = number of CDs Al has and let B = number of CDs Bea has.
We want to determine the value of B – A

(1) We can create the equation 2(B-9) = A+9
Simplify this to get 2B-18= A+9
Or 2B-A=27
This does not tell us the value of B-A. INSUFF.

(2) We can create the equation B-1 = A+1+4
Simplify this to get B-A= 6
SUFF (Bea has 6 CDs more than Al has)

Answer = B

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sanjay_dce: Senior | Next Rank: 100 Posts; Posts: 38; Joined: Tue Jan 27, 2009 10:24 am

Re: Bea's CDs

by sanjay_dce » Fri Jan 30, 2009 11:03 pm

Brent Hanneson wrote:Bea owns how many more CDs than Al owns?
(1) If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns.

(2) If Bea gives 1 CD to Al, and Al purchases 4 additional CDs, then Al and Bea will have an equal number of CDs.

Please note that this is not an official GMAT question; it’s my attempt to create difficult (650+ level) GMAT-style questions for this forum.

an easy/quick way to solve such kind of DS question is:
the question stem ask about diff b/w B and A.

1) stmt1 gives an equation but in multiple terms of one of the variable A hence A-B can't be found out( no common factor)
2) stmt 2 gives a equation where there is no multiplier of A or B hence B-A can be found out. it will take 5-10 seconds atmost if such thinking is realised

hence Ans is B

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by vikram_k51 » Tue Feb 03, 2009 7:37 am

Bea owns how many more CDs than Al owns?
(1) If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns.

(2) If Bea gives 1 CD to Al, and Al purchases 4 additional CDs, then Al and Bea will have an equal number of CDs.

From A: 2x-y=27;Not Sufficient

From B: x-y=6;Sufficient

Hence B

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