1985 AMC 8 Problem 18

Attempt Problem 18 of the 1985 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 1985 AMC 8 solutions, or check the answer key.

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

18.

Nine copies of a certain pamphlet cost less than $10.00\$10.00 while ten copies of the same pamphlet (at the same price) cost more than $11.00.\$11.00. How much does one copy of this pamphlet cost?
$1.07\$1.07
$1.08\$1.08
$1.09\$1.09
$1.10\$1.10
$1.11\$1.11
Answer: E
Concepts:inequalitybounding to limit cases
Small hint:
Let the price be p;p; then 9p<109p \lt 10 and 10p>1110p \gt 11
Big hint:
Combine into 1.10<p<1.111…1.10 \lt p \lt 1.111\ldots and find the price in whole cents
Solution:
From 9p<109p \lt 10 we get p<1.111…,p \lt 1.111\ldots, and from 10p>1110p \gt 11 we get p>1.10.p \gt 1.10.
The only price in whole cents between $1.10\$1.10 and $1.111…\$1.111\ldots is $1.11.\$1.11.
Thus, the correct answer is E .
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