(Q). In how many ways 2 rooks can be placed on a chessboard such that they are not in attacking position?
Solution:-
We know that rooks can attack only in same row or in same column.
The first rook has 64 options to be placed & since the second rook can not be placed in the same row or the same column with first rook.
So it has 7 rows & 7 columns left for it & it can be placed in 7×7 = 49 ways.
But the order in which the rooks are placed is not important. So, it will be divided by 2!
∴ total number of ways
=
= 1568 Answer
