Re: ISI 2017 key

Posted by ElPsyCongroo on May 16, 2017; 8:57am
URL: http://discussion-forum.276.s1.nabble.com/ISI-2017-key-tp7604137p7604194.html

The one with Mr. A no?

So p(Sell to all) = 1-p(Not sell to all)

It's possible to solve it from this point because if you think about it, the only way he won't be able to sell tickets to everyone is if the 2-rupee guy is first in line, (otherwise he'll have enough 1 rupee coins with him to give the guy change).

So, the probability of the 2rs. guy being first is (number of ways 2rs. guy can be first)/(total number of arrangements).

So that's (n-1)!/(n)!=1/n

So answer is 1-1/n = (n-1)/n, I think that should be right.