100 W = 100 joules per second
1 watt hours = 3600 joules
The electric bulb is lighted for 5 hours daily,
100 W × 5 = 500 watt hours
500 watt hours = 1800000 joules
1 kWh = 3600000 joules
Units consumed per day = \(\frac{1800000}{3600000}\) = 0.5 units
Untis consumed in month = 0.5 × 31 = 15.5 units …. (1)
Now, Sum of power of four 60 watt bulbs = 240 W
240 W × 5 hours = 1200 watt hours
1200 watt hours = 4320000 joules
Energy consumed per day =\(\frac{4320000}{3600000}\) = 1.2 units
Energy consumed in a month = 1.2 × 31 = 37.2 units …. (2)
Total energy consumed in a month = 15.5 + 37.2 = 52.7 units
1 unit = 1 kWh
The energy consumed in the month of January = 52.7 kWh.