Question:

There are three boxes, one contains only apples, one contains only oranges, and one contains both apples and oranges.

The boxes have been incorrectly labeled such that no label identifies the actual contents of the box it labels. Opening just one box, and without looking in the box, you take out one piece of fruit. By looking at the fruit, how can you immediately label all of the boxes correctly? 

Answer:

Take out the fruit from the box labelled ‘ Apple & Orange’.Since all labels  on the boxes are incorrect – the fruit pulled out will be either Apple or Orange.

E.g. The fruit pulled was Apple so the box will be marked ‘Apple only’.  Next, take out fruit from box labelled ‘ Apple’ .One of the two remaining boxes must be the “Orange Only” box. However, one of them is labelled “Apple”, and the other is labelled “Orange”. Therefore, the one labelled “Apple” is the box that contains only oranges, and the box labelled “Orange” is the box that has both  fruits.