a. 9*0.04*300/1000 = 0.108kWh.
C = 0.50/0.108 = $4.63/kWh.
b. C = 0.07/kWh * 0.108kWh = $0.00756
A transistor radio operates by means of a 9.0 V battery that supplies it with a 40 mA current.
(a) If the cost of the battery is $0.50 and it lasts for 300 h, what is the cost per kWh to operate the radio in this manner?
(b) The same radio, by means of a converter, is plugged into a household circuit by a homeowner who pays 7 cent per kWh. What does it now cost to operate the radio for 300 h?
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