1993 AMC 8 Problem 23

Attempt Problem 23 of the 1993 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1993 AMC 8 solutions, or check the answer key.

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

23.

Five runners, P,P, Q,Q, R,R, S,S, T,T, have a race, and PP beats Q,Q, PP beats R,R, QQ beats S,S, and TT finishes after PP and before Q.Q. Who could not have finished third in the race?
PP and QQ
PP and RR
PP and SS
PP and TT
P,P, SS and TT
Answer: C
Concepts:logical deduction
Small hint:
PP finishes ahead of Q,Q, R,R, and T,T, while QQ finishes ahead of S;S; determine PP’s place
Big hint:
If several runners must all finish ahead of a given runner, that runner cannot be as high as third
Solution:
Since PP beats QQ and R,R, finishes ahead of T,T, and QQ beats S,S, runner PP finishes first and so cannot be third.
The clues give the chain PP before TT before QQ before S.S. So P,P, T,T, and QQ all finish ahead of S,S, meaning SS is no better than fourth and cannot be third either.
Each of Q,Q, R,R, TT can finish third: for example P,P, T,T, Q,Q, R,R, SS puts QQ third; P,P, R,R, T,T, Q,Q, SS puts TT third; and P,P, T,T, R,R, Q,Q, SS puts RR third. So only PP and SS cannot be third.
Thus, the correct answer is C .
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