2003 AMC 10B Problem 15

Below is the professionally curated solution for Problem 15 of the 2003 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2003 AMC 10B solutions, or check the answer key.

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Concepts:basic countinginvariant

Difficulty rating: 1280

15.

There are 100100 players in a singles tennis tournament. The tournament is single elimination, meaning that a player who loses a match is eliminated. In the first round, the strongest 2828 players are given a bye, and the remaining 7272 players are paired off to play. After each round, the remaining players play in the next round. The match continues until only one player remains unbeaten. The total number of matches played is

a prime number

divisible by 22

divisible by 55

divisible by 77

divisible by 1111

Solution:

Each match eliminates exactly one player. Since 100100 players start and all but the champion are eliminated, there are 9999 matches.

Because 99=911,99=9 \cdot 11, it is divisible by 1111 but satisfies none of the other options.

Thus, the correct answer is E.

Problem 15 in Other Years