5. A pile contains 50 stones. Two players take turns adding from 1 to 9 stones to it. The player who brings the total number of stones to 200 wins. Who will it be - the first or the second?
5. Answer: the second wins.

The second has a winning strategy. The second can always complement the first's move to make the sum 10. Therefore, after the first's move, the last digit will be non-zero, and after the second's move, it will be zero. With this strategy, the second always has a move as long as there are fewer than 200 stones, and every time there are fewer than 200 stones after the second's move, there will still be fewer than 200 stones after the first's next move.