Question

A website requires a 7-digit password. How many different passwords can be made using the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 if each number can only be used once?

A. 120
B. 70
C.5,040
D. 604,800

Answer 1

Since order matters when making a password, this is a permutation.
There are 10 digits to chose from, so we'll start writing our equation like this:
10!/(10-r)!
It's a 7 digit password, so we'll write this:
10!/(10-7)!
And then solve:
10!/3!
3628800/6
604800
There are 604800 possible passwords, making D the correct answer