In a certain city, electricity costs $0.11 per kW middot h. What is the annual c
ID: 474665 • Letter: I
Question
In a certain city, electricity costs $0.11 per kW middot h. What is the annual cost for electricity to power a lamppost for 7.50 hours per day with (a) a 100, -watt incandescent light bulb (b) an energy efficient 25-watt fluorescent bulb that produces the same amount of light? Assume 1 year = 365 days. (c) A typical incandescent bulb costs $0.89 and lasts for a boot a year, a typical energy efficient fluorescent bulb costs about $3.49 and lasts tor about 3 years. Is the additional cost of the fluorescent bulb justified?Explanation / Answer
In a certain city, electricity costs $0.11 per kW·h. What is the annual cost for electricity to power a lamp-post for 7.50 hours per day with
(a) a 100.-watt incandescent light bulb
(a)
(365 days/yr) x (7.50 hrs/day) x (0.100 kW) x ($0.11/ kWhr) = $30.11 / yr
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(b) an energy efficient 25-watt fluorescent bulb that produces the same amount of light? Assume 1 year = 365 days. c
(b)
25 w is one-fourth of 100w, so the annual cost would be one quarter of the previous cost:
=$30.11 / 4 = $7.52
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(c) A typical incandescent bulb costs $0.89 and lasts for about a year; a typical energy efficient fluorescent bulb costs about $3.49 and lasts for about 3 years. Is the additional cost of the fluorescent bulb justified?
YES
since second number is smaller than cost of bulb is indeed justified
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