Q20 Talent Test

0 votes

Consider an 8X8 chess board. The number of ways 8 rooks can be placed in the board so that no 2 rooks are in a same row or column?

(A) 40,320

(B) 80,640

(C) 5040

(D) 720

asked Apr 8, 2017 in Aptitude by getgatebook (33,590 points)
reshown Apr 9, 2017 by getgatebook

1 Answer

+1 vote

(A)

 

We can solve this by using either rows or columns approach. Lets do by rows. For 1st row we, have 8 options to place the 1st rook. For 1st row, we have 8 choices, for 2nd row 7 choices and so on...so 8! = 40320.

Note that we should not count possibilities by BOTH rows and columns as they give us the same set of 8!

possibilities.

answered Apr 9, 2017 by (360 points)
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