A refrigerator rated 400 W operates 8 hours/day. What is the cost of the energy to operate it for 30 days at Rs 300 per KWh?

Power of the electric refrigerator, 
$$\begin{gathered} \mathrm{P}=400\mathrm{W}=\frac{400}{1000}\mathrm{KW}=0.4\mathrm{KW} \\ \mathrm{Time} \mathrm{for} \mathrm{which} \mathrm{the} \mathrm{refrigerator} \mathrm{operates} \\ \mathrm{t}=30\times 8\mathrm{h}=240\mathrm{h} \\ \mathrm{Energy} \mathrm{consumed} =\mathrm{p}\times \mathrm{t} \\ =0.4\mathrm{KW}\times 240\mathrm{h} \\ =96\mathrm{KWh} \\ \mathrm{Cost} \mathrm{of} \mathrm{the} \mathrm{energy} \mathrm{to} \mathrm{operate} \mathrm{refrigerator} \mathrm{at} \mathrm{a} \mathrm{rate} \mathrm{of} 3.00/- \mathrm{per} \mathrm{KWh} \\ =96\times 3.00=288.00/- \end{gathered}$$