] At any place, 0∕1∕2 means 0,1 or 2 will be the element at that place. Hence there are total 27=3×3+3×3+3×3) matrices of the above form. Out of which the matrices which are singular are [
0
0∕1∕2
0
0
],[
0
0
1∕2
0
],[
1
1
1
1
],[
2
2
2
2
] Hence there are total 7(=3+2+1+1) singular matrices. Therefore number of all non-singular matrices in the given form =27−7=20