Question

a hot water heater used 2.2 kilowatt for 0.5 of an hour. if electricity costs $0.06 per kilowatt-hour, how much did it cost (in dollars, to the nearest penny) to use the hot water heater?

Answer 1

$0.07 to the nearest penny.

Explanation:

We can use the units to help guide us to an answer.

Given:

2.2 kw (kilowatt) water heater power requirement

0.5 hour of hot water heater use

$0.06/kw*h is the charge for 1 kilowatt (kw) for 1 hour(h).

The power consumed by the heater in 0.5 hour is (2.2 kw)*(0.5 h) = 1.1 kwh

Multiply the power consumed by the cost:

(1.1 kwh)*($0.06/kw*h) = $0.066 or $0.07 to the nearest penny.

Note that the kwh terms cancel, leaving only $, the desired unit.