Posted by rishabh on .
Consider a 25×25 grid of city streets. Let S be the points of intersection of the streets, and let P be the set of paths from the bottom left corner to the top right corner of which consist of only walking to the right and up. A point s is chosen uniformly at random from S and then a path p is chosen uniformly at random from P. Over all (s,p) pairs, the probability that the point s is contained in the path p can be expressed as ab where a and b are coprime positive integers. What is the value of a+b?
Details and assumptions
There are 25 streets running in each direction, so S consists of 625 intersections.

maths 
ok,
where did you get this question?

maths 
Anonymous,
It comes from an Olympiad Maths problem

maths 
ok,
Can I have a link please?

maths 
Anonymous,
It does not have a link.
It is on paper. 
Cheaters 
ok,
Ok.
These are lame cheaters.
DO not provide them answers. 
maths 
ok,
SOlved.

maths 
not OK,
to ok. if you want to answer this on the site brilliant, you can by making an account but unfortunately, in every account, they have different sets of question basing on the level what you are in. this is such a very easy question.

maths 
ok,
Share your link, as I cannot create an account.

maths 
ok,
Well my answer is 49/625