Hollowatt despised power, birth and property, and announced that he would marry his smart and beautiful daughter to someone who could answer three questions correctly. One of them is about mathematics: there are two mail buses from city A to city B every day, and there are two mail buses from city B to city A at the same time. It takes 10 days for one mail bus to complete a trip. How many people can a mail car meet on the way from city A to city B?

Answer: 2* 10=20 vehicles.

The second one:

In ancient times, there was a king who loved playing chess. Before he died, he was most worried about which of his three sons his huge fortune should belong to. He decided that his three sons could play chess from now on, and his property would be given to the son whose chessboard number was exactly half of his survival days. Both the eldest son and the second son refused, saying that they didn't know how long their father would live. The younger son accepted, how can he obey his father's wishes?

A: First of all, he played a few chess games, which is exactly half of the number of days the king has lived so far. Then, every two days the king lived, he played a game of chess.

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