Question

Thane is the 20^th station from C.S.T. If a passenger can purchase a ticket from any station to any other station, how many different ticket must be available at the booking window?

Answer 1

Taking CST as first station and Thane as 20^th, let us name CST as A₀ next station as A₁ and so on, Thane is A₂₀
From station A₀, 20 different journeys are possible
From station A₁, 20 different journeys are possible.
From station A₂₀ , 20 different journeys are possible.
Total number of different tickets of different journeys
= 21 × 20
= 420