What is the cost of running seven 40 W lamps and five 80 W lamps for 12 hours of the electrical energy cost N7.00kWh?
A
N80.00
B
N45.36
C
N65.00
D
N57.12
Verified Correct Answer: D.
Physical Principles & Numerical Solution
Seven 40W lamps = 7 \times 40 = 280W
Five 80W lamps = 5 \times 80 = 400W
Total power = 280W + 400W
= 680W
= \(\frac{680KW}{1000}\) = 0.68KW
The kilowatt hour = 0.68 KW \times 12 hrs
= 8.16 KWh
Cost is N 7 per KWh
So the cost of running them = 8.16KWh \times N 7/KWh
= 57.12
Source: Myschool Past Questions Archive (Record #46442)