For better understanding, let's break this down further. Let us say you are charged N20 Kw/Hr.
Here are approximate power ratings of some domestic appliances:
Energy Lamp: 20w
Flat screen TV: 200w
Ceiling Fan: 200w
Big Fridge: 400w
Big Freezer: 800w
A. C.: 1,200w
Now, let us say in a day, a family leaves 5 energy lamps on for 10 hours, Big freezer on for 10 hours, TV for 5 hours and you use your Iron for 2 hours; here is what you will pay for that day.
Energy consumed is calculated as follows:
Lamp is 5*20=100w or 0.1Kw Charge for 10 hours is 20*10*0.1=N20
Freezer is 800= 800/1,000= 0.8Kw so Charge for 10 hours is 0.8*20*10= N160
TV is 200=200/1,000=0.2Kw So charge for 5 hours is 0.2*5*20= N20
Iron is 1,000 = 1,000/1000=1Kw So the charge for 2 hours is 1*20*2= N40.
We then add together as 20+160+20+40 =N240 for that day.
Now you know the secret!
I hope the Maths is simple enough?
@ Tunde Y. Salihu, 2016