One of the 3 boxes shown below has a question paper inside it. Above every box, there is a note attached and only one note on one of the boxes, has a true statement written.
First and second boxes say that the question paper is not in here while the third box says that the first box has the question paper.
Which box has the question paper?
According to the question stem, only one of the notes is true. If we consider the note on the third box to be true that will also imply that the note on the second box is true, and both of these notes would mean that the question paper is in the first box, but it is already given in the stem that only one of them is true. Therefore, the note on the third and the second box is false, and thus, the question paper must be in the second box.