Today, intra-city cab services are provided with aid of mobile apps. So to promote usage of their apps they have following condition and offer:
If you install the app, you need to register your app with your mobile number and you can’t register with your mobile number more than once. You suggest the app to others and those people who use your reference code in registration, get a free ride. Once the people using your reference code avail their first free ride, you get a complementary free ride (corresponding to each person). So, every time a person avail a free ride using your reference code, you get a free ride!
Now my problem for you is:
There are people (each having only one mobile number) acquainted to each other and want to exploit this offer of free rides. What is the maximum number of free rides this group of people can enjoy?
You can post you solution in comments, I will post my solution later. Happy puzzling.