tipping eco

In most restaurants, waiters receive a large portion of their compensation through tips from customers. Generally, the size of the tip is decided by the customer. However, many restaurants require a 15 percent tip for parties of eight or more. (A) Why the practice of tipping has emerged as a major method of compensating the wait staff? (B) why the customer typically decides on the amount of the tip? and (C) why restaurants require tips from large parties?