How many one-to-one correspondences exist between A = {1, 2, 3, 4} and B = {a, b, c, d}

There are 24 different correspondences.

Step-by-step explanation:

A one-to-one correspondence means that each element of A can be mapped into only one element of B, and we can't have two or more elements from A mapped into one element from B.

So, to count all the possible combinations, we need to find the number of possible options for each mapping

The first element from A, the 1, can be mapped into any of the four elements of B, so here we have 4 options.

The second element from A, the 2, can be mapped into any of the remaining elements from B, 3 of them (remember that one of the elements of B is taken).

The third element from A, the 3, can be mapped into any of the remaining elements from B, 2 of them now, so here we have 2 options.

The final element from A, the 4, can be mapped into the remaining element from B, so here we have only one option.

The total number of different correspondences (or combinations) is equal to the product between the numbers of options, this is:

Combinations = 4*3*2*1 = 12*2 = 24

There are 24 different correspondences.