2016 AMC 8 Problem 18

Attempt Problem 18 of the 2016 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2016 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

18.

In an All-Area track meet, 216216 sprinters enter a 100100-meter dash competition. The track has 66 lanes, so only 66 sprinters can compete at a time. At the end of each race, the five non-winners are eliminated, and the winner will compete again in a later race.
How many races are needed to determine the champion sprinter?
36 36
42 42
43 43
60 60
72 72
Answer: C
Concepts:basic counting
Small hint:
Think about how many sprinters are eliminated in each race.
Big hint:
To leave one champion from 216216 sprinters, all but one sprinter must be eliminated.
Video solution:
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Written solution:
Note that each race eliminates 55 people. For there to be a winner, 215215 must be eliminated. Therefore, 2155=43\frac{215}{5} = 43 races are required to eliminate this number of people.
Thus, C is the correct answer.
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