Problem:
How many four-digit positive integers have at least one digit that is a or a ?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
There are four-digit positive integers. For those without a or , the first digit could be one of the seven numbers , or , and each of the other digits could be one of the eight numbers , or . So there are
four-digit numbers with at least one digit that is a or a .
The problems on this page are the property of the MAA's American Mathematics Competitions