A telephone company in a town has 500 subsribers on its list and collects fixed charges of Rs. 300/- per year form each subsriber. The company proposes to increase the annual charges and it is believed that for every increases of Rs. 1/0, one subsriber will discontinue service. Find what increase will bring maximum revenue?

In each of the following problems, clearly state what the relevant and irrelevant factors are while going through Steps 1, 2 and 3 given in this chapter :- Suppose a company needs a computer for some period of time. The company can either hire a computer for Rs 2,000 per month or buy one for Rs 25,000. If the company has to use the computer for a long period, the company will pay such a high rent, that buying a computer will be cheaper. On the other hand, if the company has to use the computer for say, just one month, then hiring a computer will be cheaper. Find the number of months beyond which it will be cheaper to buy a computer.