There are 18 stations between Hyderabad and Bangalore. How many second class ticket have to be printed, so that passenger can travel from one station to any other station?
The total number of stations = 20
From 20 stations we have to choose any two stations and the direction of travel (i.e., Hyderabad to Bangalore is different from Bangalore to Hyderabad) in ²⁰P₂ ways.