Question

If the incandescent 100 - watt light bulb is left on for 168 hours ( a whole week),and it costs $0.12 per kwh ,how much does it cost for this lightbulb?A: $20.20B: $2.02 C:20.16D: $0.16

Answer 1

Suppose that the light bulb consumes 100W per hour, in other words, 0.1kWh. Therefore, in 168 hours, the total energy consumption is

`0.1\text{kWh}\cdot168\text{hrs}=16.8kW=16.8\cdot1000W=16800W`

Thus, the total cost is

`0.12\cdot16.8=2.016\approx2.02`

The answer is, approximately $2.02, option B.