A customer forgets a four - digit code for an Automatic Teller Machine (ATM) in a bank. However, he remembers that this code consists of digits 3, 5, 6 and 9. Find the largest possible number of trails necessary to obtain the correct code.
In the question, we have to find the possible number of 4 digit numbers formed by the numbers 3, 5, 6, 9 when repetition of digits is not allowed.
We will use the concept of multiplication because there are four sub jobs dependent on each other because a number appearing on any one place will not appear in any other place because all the four numbers are to be used as they are in the code.
The first position from the left will have four choices; the second position will have three choices because one number is consumed in the first position , the number of choices will decrease by one as we keep on going right side.
The number of ways in which we can form four-digit numbers with the help of given data is 4 × 3 × 2 × 1 = 24