# Math questions (science related)? Please help..Thanks!?

1) A 100-watt incandescent light bulb is left on in a bedroom two days every week for a year. If electricity costs 12¢ per kWh, how much extra does this cost the family this year?

2) The average energy used by an American in a year is 7.5 TOE (ton of oil). What is the average power consumption of an average American family of four in watts?

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1) A 100-watt incandescent light bulb is left on in a bedroom two days every week for a year. If electricity costs 12¢ per kWh, how much extra does this cost the family this year?

cost = 100w * 2day/week * 52wk/yr * 24hr/day * 1kw/1000w * \$0.12/kwh

cost = \$29.952/year <––––––

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2) The average energy used by an American in a year is 7.5 TOE (ton of oil). What is the average power consumption of an average American family of four in watts?

From wikipedia: https://en.wikipedia.org/wiki/Tonne_of_oil_equival...

1 TOE = 11.63 megawatt-hours

7.5 TOE = 11.63 * 7.5 = 87.225 mwh

Power = 87.225mwh * 1day/24hr * 1 year/365day * 1000kw/1mw

Power = 9.957 kw

4 people

power = 4 * 9.957

power = 39.828 kw <––––––

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Note: Many people incorrectly interchange power and energy, but they are different units.

Power is watts. Energy is watt-hours.

Example:  60 watts is the power required to operate a 60 watt light bulb.

The energy it uses in 10 hours would be 600 watt-hours or .6kwh

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