Hi please anyone help me with this question, its a combination of Permutations&Combinations and Determinants.

Q. There is a 3X3 determinant in which each element is either 1 or 0. It is given that aij = aji . There are total seven 1s in this determinants. How many such Determinants are possible?

(Answer : 6 )

Please give me an easy solution.

Thanks