2005 AMC 8 Problem 22

Attempt Problem 22 of the 2005 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 2005 AMC 8 solutions, or check the answer key.

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

22.

A company sells detergent in three different sized boxes: small (S), medium (M) and large (L). The medium size costs 50%50 \% more than the small size and contains 20%20 \% less detergent than the large size. The large size contains twice as much detergent as the small size and costs 30%30 \% more than the medium size. Rank the three sizes from best to worst buy.
SMLSML
LMSLMS
MSLMSL
LSMLSM
MLSMLS
Answer: E
Concepts:percentageratio and proportion
Small hint:
Choose convenient numbers for the small and large sizes.
Big hint:
Compare price per ounce for each size.
Solution:
Choose convenient values: let the small box cost $1.00\$1.00 and contain 1010 ounces. Then the large box contains 2020 ounces.
The medium box costs $1.50\$1.50 and contains 20%20\% less than the large box, or 1616 ounces. The large box costs 30%30\% more than the medium, or $1.95\$1.95.
The costs per ounce are S:1.0010=0.100S: \frac{1.00}{10}=0.100, M:1.5016=0.09375M: \frac{1.50}{16}=0.09375, and L:1.9520=0.0975L: \frac{1.95}{20}=0.0975.
From best to worst buy, the order is M,M, L,L, SS.
Thus, E is the correct answer.
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