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
Verified Correct Answer: D.
Physical Principles & Numerical Solution
Total power in watt = \(60\times5 + 4\times100\)
= 300 + 400
= 700W
Total power in kilo watt = 700/1000
= 0.7kW
Unit of electricity in kilowatt-hour
= 0.7 * 20hrs
= 14 okwh
i.e If I kwh costs # 10.00
14kwh = \(10.00 \times14\) = #140
Source: Myschool Past Questions Archive (Record #7298)