A square is divided into 9 identical smaller squares. Six identical ***** are to be placed in these smaller square such that each of the three rows gets at least one ball (one ball in one square only). In how many different ways can this be done?
(a) 27 (b) 36 (c) 54 (d) 81
(d) Total number of ways in which 9 ***** occupy any of the 6 squares = 9C6 = 84
Number of ways in which one row is not filled = 3
∴ Number of ways in which at least one ball occupies each row = 84 – 3 = 81
