If a student leaves 100-w lightbulb on in his room for 1 h, how many kilowatt-hour of electricity does the bulb use? if the company charges $0.18 per kilowatt-hour, how much will it cost to leave the light bulb on for this amount of time?

1)  0.1 kWh

Explanation:

The power of the lightbulb is:

The energy used by the lightbulb is equal to the product between the power (P) and the time (t):

Since the bulb has been left on for t = 1 h, the total electrical energy used is

2) $ 0.018

Explanation:

The company charges $0.18 per each kilowatt-hour. So, we can find the total cost charged for using 0.1 kWh of electricity by setting the following proportion:

$0.18 : 1 kWh = x : 0.1 kWh

And solving for x, we find