Question

an electric refrigerator rated 400w operates 8hours/day what is the of energy to operate it for 30 days at Rs 3.00 per KWH

Answer 1

Energy = Power × time × cost
=400×8×30×3/1000 ( we divide it by thousand to make it in kwh)
=288000 J. / 1000
=288 Rs.

Answer 2

We have,

Power = 400 W = 0.4 Kw

Time = 8 hours

Now,

Energy consumed in one day = power x time

                                                  = 0.4 x 8

                                                  = 3.2 KwH

Again,

amount of energy consumed in 30 days = 30 x 3.2 = 96 KwH

So,

amount to be paid per KwH = Rs. 3

=> Amount to be paid for 96 KwH = Rs. 288.

Hence the total amount to be paid is Rs. 288.