A four-digit serial number is to be created from the digits 0 through 9. How many of these serial numbers can be created if 0 can not be the first digit, no digit may be repeated, and the last digit must be 5?
1 Answer
Aug 17, 2016
Explanation:
Consider the number of options for each position.
First digit: not 0, not 5. there are 8 options.
Second digit: not 5. not the first digit. 8 options
Third digit: not 5,not 1st or 2nd: 7 options.
Fourth digit: 5. 1 option
Number of unique numbers =