2004 AMC 8 Problem 13

Attempt Problem 13 of the 2004 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 2004 AMC 8 solutions, or check the answer key.

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

13.

Amy, Bill and Celine are friends with different ages. Exactly one of the following statements is true.
I.\mathrm{I}. Bill is the oldest.
II.\mathrm{II}. Amy is not the oldest.
III.\mathrm{III}. Celine is not the youngest.
Rank the friends from the oldest to youngest.
Bill, Amy, Celine
Amy, Bill, Celine
Celine, Amy, Bill
Celine, Bill, Amy
Amy, Celine, Bill
Answer: E
Concepts:logical deductioncasework
Small hint:
If Bill were oldest, check how many statements would be true.
Big hint:
After ruling out the oldest person, use the fact that exactly one statement is true.
Solution:
If Bill were oldest, then statements I\mathrm{I} and II\mathrm{II} would both be true, so Bill is not oldest.
If Celine were oldest, then statements II\mathrm{II} and III\mathrm{III} would both be true, so Celine is not oldest.
Therefore Amy is oldest. Statements I\mathrm{I} and II\mathrm{II} are false, so statement III\mathrm{III} must be the single true statement. Thus Celine is not youngest, leaving Bill youngest.
The order is Amy, Celine, Bill.
Thus, E is the correct answer.
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