It is known that the set a = {12345} B = {678} (1) maps from a subset of B to a, of which one-to-one mapping is Known set a = {12345} B = {678} (1) Mapping from a subset of B to a, one by one mapping is (2) In the mapping from a to B, there is exactly one element in B In the mapping from a to B, one element in B has no original image

It is known that the set a = {12345} B = {678} (1) maps from a subset of B to a, of which one-to-one mapping is Known set a = {12345} B = {678} (1) Mapping from a subset of B to a, one by one mapping is (2) In the mapping from a to B, there is exactly one element in B In the mapping from a to B, one element in B has no original image

It seems that your question has not been finished. I thought it was the corresponding number
If it's really a number, do it as follows
But the first one is permutation
(1) In the subset of a = {12345}, there are three elements C5, 3 = 10, and each of them can establish 3 = 6 one-to-one mapping with B
So, according to the principle of step-by-step counting, the answer is 60
(2) In the mapping of a = {12345 to} B = {678}, there should be only three answers to exactly one element in B? All to 6, all to 7, all to 8
I don't know if there is any problem with my understanding
The key of mapping is to grasp that every element in a has the unique feature of image

How many different orders are there for the numbers 12345?
We need to calculate the process
What's more, how many permutations start with 3 and can't be followed by 2 and death?
It's the same process

5*4*3*2*1=120
2*3*2*1=12

Let u = {a, B, C, D}
In order to select two different subsets from the subset of set u = {a, B, C, D}, the following two conditions should be satisfied at the same time: (1) both a and B should be selected; (2) for any two selected subsets A and B, a must belong to B or B to a, so there are several different selection methods

There are eight different choices