Question

In a certain city, electricity costs $0.15 per kwh. what is the annual cost for electricity to power a lamp post for 6.5 hours per day with a 100 watt incandescent light bulb

Answer 1

solution:

$power consumption in 1 day=100\times 6.5\times365\\=237250watt hour\\1 watt hour=0.001kw hour\\so,237250kw hour=237.25\\1watt hour=\ 0.15\\so,237.250kw hour=237.25\times 0.15=\ 35.58$