Problem Solving

Hi All,

We're told that A and B are two partially filled buckets of water; if 5 liters are transferred from A to B, then A would contain one-third of the amount of water in B, but if 5 liters are transferred from B to A, then B would contain one-half of the amount of water in A. We're asked for the number of liters of water in Bucket A. This question can be solved in a couple of different ways, including by TESTing THE ANSWERS.

Let's TEST Answer B: 13 liters
IF.... Bucket A currently holds 13 liters of water...
then transferring 5 liters from A to B would leave 13-5 = 8 liters in Bucket A
and A would contain 1/3 of the amount in B, so B would equal 24 liters.
Thus, A STARTED with 13 liters and B STARTED with 24 - 5 = 19 liters
Transferring 5 liters from B to A would give us...
19 - 5 = 14 liters in Bucket B
13 + 5 = 18 liters in Bucket A
The amount in B is NOT exactly 1/2 of what is in Bucket A, so this is NOT the correct answer. There are two ways to 'fix' this issue: either decrease the starting amount in Bucket B or increase the starting amount in Bucket A. Increasing the amount in Bucket A would lead to a significant increase in the starting amount in Bucket B though (after transferring 5 liters from A to B, Bucket A ends up having 1/3 of the amount in Bucket B), so it's likely that we need to DECREASE the starting amount in Bucket A...

Let's TEST Answer A: 11 liters
IF.... Bucket A currently holds 11 liters of water...
then transferring 5 liters from A to B would leave 11-5 = 6 liters in Bucket A
and A would contain 1/3 of the amount in B, so B would equal 18 liters.
Thus, A STARTED with 11 liters and B STARTED with 18 - 5 = 13 liters
Transferring 5 liters from B to A would give us...
13 - 5 = 8 liters in Bucket B
11 + 5 = 16 liters in Bucket A
Bucket B now holds EXACTLY 1/2 of what is in Bucket A. This is an exact match for what we were told, so this MUST be the answer!

Final Answer: A

GMAT assassins aren't born, they're made,
Rich