1991 AMC 8 Problem 19

Attempt Problem 19 of the 1991 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 1991 AMC 8 solutions, or check the answer key.

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

19.

The average (arithmetic mean) of 1010 different positive whole numbers is 10.10. The largest possible value of any of these numbers is
1010
5050
5555
9090
9191
Answer: C
Concepts:meanextremal argument
Small hint:
The ten numbers must sum to 10×10=10010 \times 10 = 100
Big hint:
To make one number as large as possible, make the other nine as small as possible: 1,2,…,91, 2, \ldots, 9
Solution:
The ten numbers sum to 100.100. To maximize one of them, the other nine (all different positive whole numbers) should be as small as possible: 1+2+⋯+9=45.1 + 2 + \cdots + 9 = 45.
The largest number is then 100−45=55.100 - 45 = 55.
Thus, the correct answer is C .
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