Question

how many sub marix possoble in 3 by 3 matrix?​

Answer 1

To form a Sub-matrix , we have a choice for each row & column - to take or not to take.

So, total we have 2m * 2n choices ,

But we have to exclude matrix having 0 rows & 0 columns - which can be formed when we delete all rows OR All Columns , which correspond to 2m + 2n - 1 ways.