Let A = 1, 2, 3, 4 . The number of bijective functions from A to A is

The correct answer is Option (4) → 24

A bijective function from A to A gives the 4 elements 4 different images, so every element of A is used exactly once.

The image of 1 can be chosen in 4 ways, then the image of 2 in 3 ways, of 3 in 2 ways and of 4 in 1 way:

    \(4 \times 3 \times 2 \times 1 = 4! = 24\)

So there are 24 bijective functions from A to A.