The price of electricity went up by 25%. John's old computer used 800 watts and his new computer uses 50% more. If the old price of electricity was 12 cents per kilowatt-hour, how much does his computer cost, in dollars, to run for 50 hours?
Let's be accurate as possible. Think before you answer.
9
His new computer uses 800 *.

5 = 400 watts more than his old computer.

So it users 800 + 400 = 1200 watts.

That is 1200 / 1000 = 1.

2 kw.

Electricity cost 12 *.

25 = 3 cents more than it used to.

So it now cost 12 + 3 = 15 cents per kwh.

He used 1.

2 * 50 = 60 kwh.

So he paid 15 * 60 = 900 cents per kwh.

So he paid 900 / 100 = $9.

.

The answer is 9