Along a railway line, there are 20 stations. The number of different tickets required in order so that it may be possible to travel from every station to every station is what ?

Suppose the 20 stations are A,B, C, D,….. T

If you get in the train on station A, it will go to T thorough B,C,D, and so on. So, from A till T we need 20 tickets.

If you get on the train on station B, it will go to T thought C, D ,E and so on. So, from B, we need 19 tickets.

Similarly, this pattern will go on till station T where we need only 1 ticket.

Therefore the answer will be 20+19+18.. 1 = $\frac{20(20+1)}{2}=10\times 21$=210

But if you assume that the train will travel to every station from every other station, then the answer will be 20$\times$19=380