The cost of running five 60 W lamps and four 100 W lamps for 20 hours if electrical energy cost #10.00 per kwh is?

A. 280.00
B. 160.00
C. 120.00
D. 140.00

Correct Answer:

Option D – 140.00

Explanation

Total power in watt = 60*5 + 4*100
= 300 + 400
= 700w
Total power in kilo watt = 700/100
= 0.7 killo w
Unit of electricity in killo watt-hour
= 0.7 * 20hrs
= 14 okwh
i.e If I kwh costs # 10.00
14kwh = 10.00 * 14 = #140