Question

A bank ATM system has a pad with 10 digits (0 to 9). Find the number of possible 4-digit pin codes

if digits can be repeated.
if digits cannot be repeated.

a.
1. 10 000 ; 2. 5 040.

b.
1. 5 040; 2. 10 080.

c.
1. 10 000; 2. 210.

d.
1. 3 125; 2. 15 120.

Answer 1

A

Explanation:

If digits can be repeated, that means there are 10 options for each place in the pin code. 10*10*10*10 = 10,000

If digits can not be repeated, there are 10 options for the first digit, 9 options for the second digit, 8 options for the third digit, and 7 options for the fourth digit. 10*9*8*7 = 5040