A cleaning company uses 10 lbs each of chemicals A, B and C for each house it cleans. After some quality complaints, the company has decided to increase its use of chemical A by an additional 10 lbs for each house. By what % has productivity (houses per pound of chemical) fallen?
A) 0%
B) 10%
C) 15%
D) 25%
E) 33%

Question

Quizplus · Accepted Answer

Productivity in terms of houses cleaned per pound of chemical is inversely related to the amount of chemical used per house. Initially, the company used 30 lbs of chemicals in total (10 lbs each of A, B, and C) for each house. After increasing the use of chemical A by an additional 10 lbs, the total chemical usage per house becomes 40 lbs. The increase in chemical usage from 30 lbs to 40 lbs represents a 33.33% increase in chemical usage per house, which means the productivity (houses cleaned per pound of chemical) decreases by 25% because the ratio of houses cleaned per pound of chemical decreases as more chemical is used per house.

A Cleaning Company Uses 10 Lbs Each of Chemicals A