There are 4 station in between Hand B.2 people board this train by taking different tickets.In how many ways can 2 person purchase the tickets? if ur answer is 210 plz explain why 105 *2 is done.

From first station there are total 5 possible tickets. From 2nd one , 4 tickets are possible and 3rd one 3 , 4th one 2 and 5th one 1 so in total 5+4+3+2+1=15, different tickets are possible. Hence different ways possible = 15C2 = 105. In case 210 is given as the answer than question would not have mentioned the direction. So we multiply by 2 to also include cases if person goes in reverse direction.
Hope it is clear.