Problem:
An ATM password at Fred's Bank is composed of four digits from to , with repeated digits allowable. If no password may begin with the sequence , then how many passwords are possible?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
If there were no restrictions, then passwords would be possible. Among these, passwords begin with , and have options for the fourth digit. Thus passwords satisfy the condition.
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions