Seeta says that a compact fluorescent lamp uses less electrical energy compared to that of an incandescent bulb. But Geeta, her friend, does not agree with this. Seeta proves it by calculating the money that can be saved per month by using a compact fluorescent lamp of 15 W in place of an incandescent bulb of 100 W if they are used 8 hours per day for 30 days. How did she prove this? (The cost of one unit of electrical energy is Rs. 2)

Explanation

The energy consumed in operating a fluorescent lamp `= 15xx8xx60xx60xx30 J`
`=(15xx8xx36xx3xx10^(3))/(36xx10^(5))kW h = 3.6 k W h`.
The cost `= xx 3.6 = Rs. 7.2`
The energy consumed by the bulb `= 100 xx 8 xx 60 xx 60 xx 30 J`
`=(8xx36xx3xx10^(3))/(36xx10^(5)) kW h = 24 k W h`.
The cost `= 2xx24 = Rs. 48`.
Saving `= 48-7.2=Rs. 40.8`.