Hi

I have the following question and struggling:

let A be the 10-digit decimal integer, that is

A:={0000000000,0000000001,...,9999999999}

How many elements of A have exactly three o's and two 1's?

So i need to use p(a and b)= p(a) + p(b) - p(a or b)

Just struggling to find how many elements there are with exactly what is needed so i can apply it to the equation

many thanks in advance.