A company wants to decrease their energy use by 10%. If their electric bill is currently $1,500 a month, what will their bill be if they are successful? Give your answer accurate to at least the nearest dollar.

  $1350

Step-by-step explanation:

Apparently, we're to assume that the bill is proportional to the energy usage. Then reducing energy by 10% would reduce the bill by 10%.

10% of the bill is 0.1 × $1500 = $150.

If the bill is reduced by $150, it becomes ...

  $1500 -150 = $1350

If they are successful, their bill will be $1350.

In general, utility bills have a number of fixed charges or fees that are not proportional to the quantity of utility used. Too, they can have graduated rates that make them non-proportional.

Figuring 90% of some arbitrary number might be an interesting math exercise, but it has no relation to the world of utility billing for a 10% change in usage.