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

What is the cost of running seven 40 W lamps and five 80 W la mps for 12 hours of the electrical energy cost N7.00kWk?
A. N80.00
B. N45.36
C. N65.00
D. N57.12

Correct Option: Answer is D

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

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