The supplier of the hardware store has brought us three boxes, one of which contains screws, another one contains nuts and the last one is full of nails. The person who has placed the labels with the contents of each box had a bad day, has been confused to put them and has not been successful with any label. Opening a single box and taking out a single piece ...
Could you tell me how you can get each box its correct label?.
If we look closely at the statement we see that it tells us that: "it has not been right with any label." By taking a piece from one of the boxes, we know the contents of this first box. We also know that your label corresponds to one of the other boxes and that these have the wrong labels. One of the remaining boxes will have the label of the piece that we know so we take it off and place it. Since we know that all the labels are wrong, we deduce that the remaining box (to which we have not removed the label) has it incorrect and its label belongs to the one to which we have removed the label to put it in the first box, so that by elimination, the last box will contain what the label of the first box indicates.
We can see it more clearly with an example. Assume that the labels on the boxes are as follows:
Box 1 ==> Screw label ==> Content ??
Box 2 ==> Nut label ==> Content ??
Box 3 ==> Nail tag ==> Content ??
We open the box 1 that contains for example nails (surely it will not contain screws since it is what its label indicates) so we remove the label from the box 3 and place it to the box 1. Since all the labels are wrong , the label of box 2 will be incorrect and therefore must belong to box 3 (which will contain the nuts), from which we deduce that the label of box 1 will belong to box 2 (which will contain the screws).