Math CentralQuandaries & Queries


Question from Trish:

First I have to solve the problem. Then write a number sentence for the problem.
The problem: By installing a $\$120.00$ thermostat that reduces the temperature setting at night a family hopes to cut its annual fuel bill for heating oil by 8%, and recover the cost of the thermostat in fuel savings after 2years. What was the family's annual fuel bill before installing the thermostat?
Thanks can't figure this one out!

Hi Trish,

This is a situation where I would just guess, check to see if my guess is correct and see if this tells me how to proceed. I am going to guess that the family's annual heating bill is $\$1,000.00.$ If they save 8% per year how much would they save in a year? How much in two years? Write this result as a number sentence.

Now suppose the annual heating bill is $\$X.$ Write the number sentence above with the annual heating bill as $\$X$ rather than $\$1,000.00.$ Solve for $X.$

Write back if you need more assistance,

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