In a house there are four bulbs each of 50 W and 5 fans each of 60 W. If they are used at the rate of 6 hours a day, the electrical energy consumed in a month of 30 days is

Number of bulbs = 4 
Power of each bulb = 50 W
Total power $=4\times 50$
 = 200 W
Total time $=6\times 30$
= 180 h 
Energy consumed by the bulbs
 $\begin{array}{l}=200\times 180\mathrm{Wh}\\ {\mathrm{E}}_1=36\mathrm{kWh}\end{array}$
 Number of fans = 5
Power of each fan = 60 W
Total power $=5\times 60$
 = 300 W
Total time $=60\times 30=180\mathrm{h}$ 
Energy consumed by the fans
 $\begin{array}{l}=300\times 180\\ =54\mathrm{kWh}\end{array}$ 
Total energy consumed
 $\begin{array}{l}=36+54\\ =90\mathrm{kWh}\\ =90\text{ units }\end{array}$