Question: how many columns are in a 5x4 matrix?
Answer: By convention, when we say a matrix is m×n m × n if it is composed of m rows and n columns. So a 4×5 4 × 5 has exactly 4 rows and 5 columns while a 5×4 5 × 4 matrix is a matrix made of 5 rows and 4 columns. These two matrices are different.