Calculate the total cost of running the following electrical devices in the month of September, if the rate of 1 unit of electricity is Rs 6.00.

- Electric heater of 1000 W for 5 hours daily.
- Electric refrigerator of 400 W for 10 hours daily.

### Answer

P_{1} = 1000 W / 1000 = 1 kW

t_{1} = 5 h

P_{2} = 400 W / 1000 = 0.4 kW

t_{2} = 10 h

No. of days, n = 30

E_{1} = P_{1} x t_{1} x n

= 1 kW x 5 h x 30 = 150 kWh

E_{2} = P_{2} x t_{2} x n

= 0.4 kW × 10 h × 30 = 120 kWh

Total energy = (150 + 120) kWh = 270 kWh

Total cost = 270 x 6 = Rs. 1620