by what percent did the Smiths’ monthly electricity bill decrease after they moved?

Question

After their children were married, Mr. and Mrs. Smith moved from their large house in the country, were their average monthly consumption of electricity had been 1500 kilowatts-hours, to a smaller house in town, where their average monthly consumption of electricity was 800 kilowatts-hours. If the cost per kilowatt-hour of electricity was $0.08 in the country and $0.10 in town, by what percent did the Smiths’ monthly electricity bill decrease after they moved?

A. 25%

B. 33 1/3%

C. 40%

D 66 2/3%

Answer 1

Hi Ben,

 

Let's begin by computing the monthly electric bill for each house:

 

    country house bill =  (1500 kw-hrs)($0.08 / kw-hr) 

    country house bill = $120

 

    town house bill = (800 kw-hrs)($0.10 / kh-hr)

    town house bill = $80

 

Now that we know the monthly electric bill for each house, we can calculate the percentage decrease in the monthly electric bill:

    % decrease = [($120 - $80) / 120] x 100%

    % decrease = (40 / 120) x 100%

    % decrease = (1 / 3) x 100%

    % decrease = 33 1/3% (choice B)

 

This was a 2-step problem:

    1.  Compute each monthly electric bill.

    2.  Compute percentage decrease in monthly electric bill.

 

Thanks for submitting this problem and glad to help.

 

God bless, Jordan.