If electricity costs 5 kobo per unit, what is the monthly cost of operating 5 electric bulbs, each rate \(100 \mathrm{~W}\); given that the bulbs are to be on for fourteen hours daily?
A. \(\# 3.75\) B. \(\#2.10 \) C. N10.50 D. N111.1
Correct Answer: C
Explanation
Total power \(=5 \times 100 \mathrm{~W}=500 \mathrm{~W}\) \begin{array}{l} =\left(\frac{500}{1000}\right) \mathrm{KW} \\ =0.5 \mathrm{KW} \end{array} Time \(=14\) hrs \(\times 30=420 \mathrm{hrs}\) Total energy used \(=0.5 \mathrm{KW} \times 420 \mathrm{hr}\) \(=210 \mathrm{KWh}\) Since \(1 \mathrm{KWh} \operatorname{cost} 5\) kobo, the overall cost \(=(210 \times) \mathrm{kobo}=1050 \mathrm{kobo}=\mathrm{N} 10.50\)
