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You have 3 boxes, each containing two balls, one containing [#permalink]
23 Dec 2003, 17:57

00:00

A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

0% (00:00) correct
100% (03:20) wrong based on 6 sessions

You have 3 boxes, each containing two balls, one containing a black pair; one, a white pair; and the third, one white ball and one black ball. On each box are pictures of two balls - either two black ones, two white ones, or one white and one black. You are told that the markings on the boxes are all wrong. You are asked to ascertain the colors of the balls contained in each box.

Which of the following statements can be inferred from the above?

A) You can take out one ball from the box marked with two black balls and, without looking at the second ball, know what each box actually contains.
B) You can take out one ball from the box marked with two white balls and, without looking at the second ball, know what each box actually contains.
C) You can take out one ball from the box marked with one white ball and one black ball and, without looking at the second ball, know what each box contains.
D) You cannot know which balls are contained in which box until you take a ball out of more than one box.
E) You cannot know which boxes contain which color balls until you take a ball out of all three boxes.

Re: You have 3 boxes, each containing two balls, one containing [#permalink]
22 Jan 2012, 20:05

Answer should be D. You need to take out 1 ball from the box marked 1B1W. and Two from any of the other two.

BB BW >>>>>>pick one from this box. You can guess the color of second ball in this box. Which ever color is the first ball, the second ball has to be the same color. WW

After picking one ball, BB , can contain BW or WW. We can't ascertain that before taking out 2 balls from the box.

So answer choice "E" is not necessary > that you need to take one ball from each of the boxes.

A, B, C not possible. Since you cannot find out the contents of all the boxes by picking one.

Re: You have 3 boxes, each containing two balls, one containing [#permalink]
23 Jan 2012, 04:49

The answer should be C. 1) You take 1 ball from the box marked 1B1W. If it is black than obviousely it is 2B box (if white - then 2W). 2) You know exactle that box marked '1B1W' is indeed 2B. Now you may assume that 1 of the other 2 boxes (marked '2B' and '2W' is really 1B1W 3) If you assume that '2B' box is indeed 1B1W that would mean that '2W' box really contains 2 white balls which contradicts with the original task - you are told that ALL the markings are wrong. 4) That means that box marked '2W' is really 1B1W and the box marked '2B' is 2W.

Re: You have 3 boxes, each containing two balls, one containing [#permalink]
23 Jan 2012, 06:05

For me C 1. You pick up a ball from box marked WB and it's W so it's WW box. 2. You left with 2 boxes marked WW and BB,(but we have discovered the WW box) so you know that those boxes are BB or WB. 3. You know that BB box can't contain BB so it's WB and the other one is BB. Don't understand wtf OA is D

Re: You have 3 boxes, each containing two balls, one containing [#permalink]
23 Jan 2012, 07:49

Answer "C"

Step 1: Pick one ball out of the box labeled with BW --> IF B, then BB (i will go with BB) --> If W, then WW Step 2: Two boxes left labeled with BB and WW --> BB is already taken, so WW (before it could be BW and BB) can only be BW --> As BB and BW are taken now, wrong labeled box "BB" can only be WW

Thus, C

gmatclubot

Re: You have 3 boxes, each containing two balls, one containing
[#permalink]
23 Jan 2012, 07:49