12 noughts and 4 crosses are arranged in 4 rows of 4. For instance, one arrangement is:
00x0
0x0x
0000
x000
i) How many arrangements are there?
ii) How many arrangements with a cross in every row?
iii) How many arrangements are there in which there is a cross in every row and in every column?
So these are my answers, I wanted to check if they are correct:
i) 16C4 = 1820
ii) 4^4 = 256
iii) 4! = 96
I used the approach that there are 4 places to put the cross in the first column, then 3 in the 2nd, 2 in the 3rd, and 1 in