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Just wanted to share a nice problem.I have given my method below.More answers are welcome.

Consider a rectangular integral grid of size $m*n$.A person has to travel from one end say $(0,0)$ to the diagonally opposite end $(m,n)$.He moves one step at a time towards the east or towards the north(that is,never moves towards the west or south at any time).How many distinct paths exist from the point A to the point C ?

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Suppose you had to describe this path to a person who cannot see the figure,you could tell him in form of a string say: $EENENEENN$.

This string we just formed helps to realize all possible paths from one vertex to the diagonally opposite vetex. (E stands for EAST and N stands for NORTH)

So we just have to find all permutations of the string which is $\frac{(m+n)!}{m!n!}$ .

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    $\begingroup$ Indeed. This is the best method to solve it... $\endgroup$ – user276580 Oct 26 '15 at 17:59

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