I was wondering how can we can count how many available combinations in simple school locker ? And then if we can how many possible number of credit cards can be issued ?

For each piece you have 10 possibilities, the numbers 0,1,2,3,4,5,6,7,8,9.

You have four of those numbers. Hence there are 10 x 10 x 10 x 10 = 10^4 = 10.000 possibilities.

Can you now try to answer your own question for the creditcard?

Kind regards,

Lisa

“You have four of those numbers. Hence there are 10 x 10 x 10 x 10 = 10^4 = 10.000 possibilities.”

Wouldn’t the possible options be substantially higher than 10,000? If you just take 2, so 0-9 with 2 options, wouldn’t that be a factorial of 20?

So in the example of one lock, wouldn’t it be a factorial of 40, so some crazy ridiculous number?

To use the book analogy from the course, wouldn’t you have “40 books” in this scenario, just 10 on each shelf, with 4 shelves, so 40! = total number of permutations?