Open the box that is labeled "Apples and Oranges".
You know that since none of the labels are correct, the box must either contain only apples, or only oranges.
Suppose that you remove an apple from that box. Therefore, that box is the "Apples Only" box. (If, in fact, you removed an orange from the box, you can swap “Apples” and “Oranges” for the rest of the description; the same reasoning applies).
One of the two remaining boxes must be the "Oranges Only" box. The remaining two boxes are labeled "Apples Only" and "Oranges Only". Since the labels cannot match, the “Oranges Only” label cannot have “Orange Only” contents.
Therefore, the one labeled "Apples Only" is the box that contains only oranges, and the box labeled "Oranges Only" is the box that has both kinds of fruit.
You know that since none of the labels are correct, the box must either contain only apples, or only oranges.
Suppose that you remove an apple from that box. Therefore, that box is the "Apples Only" box. (If, in fact, you removed an orange from the box, you can swap “Apples” and “Oranges” for the rest of the description; the same reasoning applies).
One of the two remaining boxes must be the "Oranges Only" box. The remaining two boxes are labeled "Apples Only" and "Oranges Only". Since the labels cannot match, the “Oranges Only” label cannot have “Orange Only” contents.
Therefore, the one labeled "Apples Only" is the box that contains only oranges, and the box labeled "Oranges Only" is the box that has both kinds of fruit.