Quote:
You have three 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 block 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 is 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 is 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 is 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.
The right answer here is
C. The key to solving any inference question is that the answer you pick MUST be true. This means that if it is even
slightly possible that the statement could be false, you must eliminate.
With this question in particular, the crux of the question is that
ALL the boxes are marked wrong. Since there are only three boxes to begin with, what is in a box will only be down to one of two options.
A - If the box is marked as 2B, then it must be 1B1W, or 2W. If you get a black ball, then you know it has to be 1B1W,
but if you get a white ball, you do not know which outcome it is.
OUTB - Wrong for the same reason that A is wrong, but in inverse fashion. If you get a black ball, you don't know if its 1B1W or 2B.
OUTC - The only possibilities here are 2B and 2W. Hence, whether you get a black ball or a white one, you immediately know what the other ball must be. This answer therefore will always be true and is
CORRECT.
D - This is absolutely not correct. If you take two balls out of just one box, you know for sure what is in that box. Hence, you also know what is in the others, since the labels on them are incorrect, and you've eliminated another option by knowing the content of said box, leaving just one possibility.
OUTE - This is even more obviously wrong, based on what we've observed in D. If you don't need 2 boxes even, you certainly don't need three.
OUT - Matoo
- Matoo