A house has ten 40W and five 100W bulbs. How much will it cost the owner of the house to keep them lit for 10 hours if the cost of a unit is 5N?

To calculate the cost of keeping the bulbs lit for 10 hours, we need to determine the total energy consumed by all the bulbs in the house, expressed in units of electricity. The 40W bulbs consume 40/1000 = 0.04 kW per hour, while the 100W bulbs consume 100/1000 = 0.1 kW per hour. To calculate the total energy consumed by all the bulbs, we can multiply the power consumption of each bulb by the number of bulbs and add the results: Total power consumption = (10 bulbs x 0.04 kW/bulb) + (5 bulbs x 0.1 kW/bulb) = 0.4 kW + 0.5 kW = 0.9 kW Next, we need to calculate the total energy consumed over 10 hours: Total energy consumed = 0.9 kW x 10 hours = 9 kWh Finally, to calculate the cost of this energy, we need to multiply the total energy consumed by the cost per unit of electricity: Cost of energy = 9 kWh x 5N/kWh = N45 Therefore, the cost to the owner of the house to keep the bulbs lit for 10 hours is N45.