Suppose a 7-digit phone number is chosen at random. What is the probability that the digits are distinct (i.e. that no digits repeat)?

Answer 1

The number of distinct 7 digit numbers is (assuming all digits are acceptable) is the permutation of 10 thiings 7 at a time: 10!/3!

The number of possible numbers with replacement is 10⁷

The ratio is the probability of the event.