Rat and Elephant Ways

#1

i did not understand the permutation and combination approach quite well.Can anyone explain me?

#2

@dare_devil_007
P&C solution is basically based upon two formula of P&C.

  1. If we want to arrange n distinct items, then no of ways = (n)!
  2. If we want to arrange n items among which m are identical, then no of ways = (n)!/(m)!

So here, we want to make overall (m-1) for moving down and (n-1) for moving right steps to reach the destination, but every down move or right move is identical among themself so just divide (m-1+n-1)! by (m-1)! and (n-1)!

#3

@dare_devil_007 please mark this doubt as resovled if you are able to understand it now.

#4

why is it m-1 and n-1 while we are making m and n moves?

#5

@dare_devil_007 suppose you are (0,0) and need to reach (2,2) so you need (2-0) steps right which is m-1 and (2-0) steps down which is n-1
where n and m are 3 but index are 0-based.

I hope it is clear now.

#6

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