Adam gave half of the apples he had plus one more to Eve. He gave half of the remaining ones plus one more to Diana. Now, Adam was left with just one apple.

Can you find out how many did he have in the beginning?

10

In such type of questions we can come to a conclusion by working our way backwards.

He is left with one apple in the end. He gave half of what he had plus one to Diana. If we remove the extra one, the he must have had two apples. Since now both of them have half of the remaining ones, it must be 2 * 2 = 4 apples.

Again move back. Adam gave half of what he had plus one extra to Eve. Thus if we remove that extra one and give it back to Adam, then Adam must have 5 apples. Since he gave half to Eve, it means he must have had 5 * 2 = 10 apples in the beginning.

Thus Adam had 10 apples in the beginning