Three labelled boxes containing red and white cricket balls are all mislabelled. It is known that one of the boxes contains only white balls and another one contains only red balls. The third contains a mixture of red and white balls. You are required to correctly label the boxes with the labels red, white and red and white by picking a sample of one ball from only one box. What is the label on the box you should sample?

1) white
2) Red
3) Red and white
4) Not possible to determine from a sample of one ball

• Answer is 3.
  The first thing to do is to take a ball from the box incorrectly labeled 'red and white balls'. If it is red, then clearly this is the box containing red balls. If white, then white. Since we know that the boxes are all incorrectly labeled it is now sufficient to switch the two remaining labels.
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