A 2kW heater, a 200 watt TV and three 100 watt lamps are all switched on from 6-10PM. What is the total cost at Rupees 5.50 per kWh?

For heater, P = 2kWh T = 4 hours

Energy consumed = PT = 8kWh

For TV,

P = 200 watt = 0.2kW T = 4 hours

Energy consumed = PT = 0.8kWh

For lamps,

P = 100 watt = 0.1kW T = 4 hours

n = 3

Energy consumed = PTn = 1.2kWh

Total energy consumed = 8 + 0.8 + 1.2 = 10kWh Cost of 1kWh = Rupees 5.50

Total cost = Rupees 55.