How many combinations of eight digits can the ten numbers 0-9 form? Among them, the ten numbers 0-9 can be repeated at will. Can you list them How many digits do you have I don't think we should start with 0. We need 8 digits

How many combinations of eight digits can the ten numbers 0-9 form? Among them, the ten numbers 0-9 can be repeated at will. Can you list them How many digits do you have I don't think we should start with 0. We need 8 digits

A7 + 9 * A8 (9), 8 above and 9 below

From 0,1,..., 9, randomly take 4 numbers (repeat allowed) to arrange a column, the result just forms a four digit number. Find the probability of the following events: a = {4 numbers are not equal in pairs}; b = {this number is odd}, C = {6 appears at least once}, d = {6 appears just once}, please write down the specific steps, thanks here