Some riddles

Number 3 is easy though. Just ask for fruit from the box labelled apples & oranges. Then you can label each box correctly.
1) Since each label is incorrect, it goes to show that the fruit you pick from the box has to be either apples only or oranges only.
2) The box that this label originally came from (say, for instance the box originally labelled apples) now doesn't have a label, but since it can't be labelled with the 'apples & oranges' label (which, in effect, would mean the box with oranges in this example had been labelled correctly from the getgo, and that falsifies the original premises), it has to be the other type of fruit.
3) the third box now has to be labelled 'apples & oranges'.