What will be the total running cost of a heater of 1000W for 5 hrs daily and a refrigerator of 400W for 10 hrs daily in a month of 30 days, if the rate of 1 unit of electricity is Rs.6?

The relationship between Energy and power is 
$\mathrm{Energy} = \mathrm{Power} \times \mathrm{time}$ …(1)
For Heater:
Power $\left(\mathrm{P}\right)\mathrm{ }=\mathrm{ }1000 \mathrm{W}$
                  $=\mathrm{ }1 \mathrm{kW}$
Time $\left(\mathrm{T}\right)\mathrm{ }=\mathrm{ }5\mathrm{ }\mathrm{hrs}$
The number of days for which the appliance is used is $\left(\mathrm{n}\right)=30$
Energy consumed $\left(\mathrm{E}\right)= \mathrm{P}\times \mathrm{T}\times \mathrm{n}$
                                   $=1\mathrm{kW}\times 5\times 30$
                                   $=150 \mathrm{kWh}$
For refrigerator: 
Power $(\mathrm{P}\text{'})\mathrm{ }=\mathrm{ }400 \mathrm{W}$
                   $=\mathrm{ }0.4 \mathrm{kW}$
Time $(\mathrm{T}\text{'})\mathrm{ }=\mathrm{ }10\mathrm{ }\mathrm{hrs}$
Energy consumed $(\mathrm{E}\text{'})= \mathrm{P}\text{'}\times \mathrm{T}\text{'}\times \mathrm{n}$
                                    $= 0.4\times 10\times 30$
                                    $= 120\mathit{ kWh}$
Total energy $=(150+120)$
                     $=270 \mathrm{kWh}$
Therefore, the total cost $=270\times 6\mathrm{ }$$=\mathrm{Rs}.1620$
 The total running cost of a heater of 1000W for 5hrs daily and a refrigerator of 400W for 10hrs daily in a month, if the rate of 1 unit of electricity is Rs.6 will be Rs. 1620.