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Question

# A washing machine rated 300W is operated for one hour/day. If the cost of a unit is Rs 3.00 then the cost of the energy to operate a washing machine for the month of March is

A
Rs25.60
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B
Rs27.50
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C
Rs27.90
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D
Rs26.90
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Solution

## The correct option is C Rs27.90In this case, the washing machine that is rated 300 W is operated for 1 hr/day. The electric bill has to be calculated for the month of March. That is, the total number of hours the washing machine is operated in this month is 31 hours as this month has 31 days.The total energy that is used by the washing machine in a day is given by the formula Q=Pt.Here, the power is 300 W and the time used is 1 hour.So, Q=300W×1h=300Wh=0.3 kWhTherefore, the total number of kWh for a month is 0.3kWh×31=9.3 kWhThe cost of 1 kWh is given as Rs.3.Hence, the total cost for a month is =9.3kWh×3=Rs.27.90

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