# math

posted by
**LIZ** on
.

You are thinking of making your mansion more energy efficient by replacing some of the light bulbs with compact fluorescent bulbs, and insulating part or all of your exterior walls. Each compact fluorescent light bulb costs $4 and saves you an average of $2 per year in energy costs, and each square foot of wall insulation costs $1 and saves you an average of $0.20 per year in energy costs.† Your mansion has 200 light fittings and 3100 sq ft of uninsulated exterior wall. To impress your friends, you would like to spend as much as possible, but save no more than $850 per year in energy costs (you are proud of your large utility bills). How many compact fluorescent light bulbs and how many square feet of insulation should you purchase? How much will you save in energy costs per year? (If an answer does not exist, enter DNE.)

compact fluorescent light bulbs 1

insulation 2 ft2

total cost $ 3

energy costs savings $ 4 per year