Question

BRAINLIEST AND 39 POINTS

Answer 1

You have 10 numbers to choose from, and you're choosing 4 from that pool. Order of the numbers matters, because having 1234 as a PIN is not the same having it be 1324, so we're counting the number of permutations of 10 digits taken 4 at a time. So there are

$4!\dbinom{10}4=4!C(10,4)=4!C^{10}_4=\dfrac{10!}{(10-4)!}=5040$

possible PINs that can be made.