Paragraph: Let A be the set of all 3 3 symmetric matrices all of whose entries are either 0 or 1 . Five of these entries are 1 and four of them are 0 . Question: The number of matrices in A is

Step-by-step solution

Case I When all three diagonal elements are 1 , then Number of matrices = ^3 C₁=3 Case II When two diagonal elements are zero and one element is one no, then Number of matrices = ^3 C₁ ^3 C₁=9 Total matrices =3+9=12