What is the cost of running seven 40W lamps and five 80W lamps for 12-hours of the electrical energy cost N7.00kWk?

A. N80.00
B. N45.36
C. N65.00
D. N57.12

Correct Answer:

Option D – N57.12

Explanation

Seven 40W lamps = 7 × 40 = 280W

Five 80W lamps = 5 × 80 = 400W

Total power = 280W + 400W

= 680W

= 680KW/1000 = 0.68KW

The kilowatt hour = 0.68 KW × 12 hrs

= 8.16 KWh

Cost is N 7 per KWh

So the cost of running them = 8.16KWh × N 7/KWh

= 57.12