Bea owns how many more CDs than Al owns?

[BTGModeratorVI]

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.

Answer: B
Source: Magoosh

[Brent@GMATPrepNow]

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.

Answer: B
Source: Magoosh

Let A = number of CDs Al owns
Let B = number of CDs Bea owns

Target question: What is the value of B - A?

Statement 1: If Bea gives 9 of her CDs to Al, then Al will own twice as many CDs as Bea owns.
We can create the equation: 2(B - 9) = A+9
Expand left side to get 2B - 18 = A+9
Rearrange to get: 2B - A = 27
This does not tell us the value of B - A.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 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
We can create the equation: B - 1 = (A + 1) +4
Simplify this to get B - A = 6
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

Cheers,
Brent