Question

A customer forgets a four-digit code for an automated teller machine (ATM) in a bank. However, he remembers that this code consists of digits 3, 5, 6, 9. Find the largest possible number of trials necessary to obtain the correct code.

Answer 1

Given: code consists of digits 3, 5, 6, 9. 

To find: the largest possible number of trials necessary to obtain the correct code. 

The customer remembers that this 4 digit code consists of digits 3, 5, 6, 9. 

So the largest possible number of trials necessary to obtain the correct code = 4! = 4 × 3 × 2 × 1 = 24