What is the number of different matrices, each having 4 entries that can be formed using 1, 2, 3, 4 (repetition is allowed)?

Matrices with 4 entries can be of order 1×4, 4×1, or 2×2 (3 different orders/shapes). For each shape, each of the 4 positions can be filled in 4 ways (with repetition), giving 4⁴ = 256 matrices per shape. Total = 3 × 256 = 768.