Problem:
How many two-digit positive integers have at least one as a digit?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
There are two-digit numbers with a as their 's digit, and two-digit numbers with as their units digit. Because satisfies both of these properties, the answer is .
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions