How many minors are there of a 3x4 order matrix?

A minor is a determinant and a determinant is a value associated with a square matrix.

The matrix from which a minor is calculated is formed from a matrix by removing at least one of its rows or columns.

We are discussing matrices of 3 rows and 4 columns. The minimum change one can make is to remove a single column. This can be done in four ways, yielding four minors. Each of these four ways yields a 3x3 matrix. There are nine minors in a 3x3 matrix.

Hence, the total number of minors is 4 + 4(9)=40.