Problem:
How many four-digit whole numbers are there such that the leftmost digit is odd, the second digit is even, and all four digits are different?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
There are odd and even digits that can be used for the two leftmost digits in the number. Once an odd and even digit have been selected and since all four digits are different, there are choices remaining for the third digit, and then choices for the fourth digit. Thus there are such whole numbers.
Query. How many four-digit whole numbers have an even leftmost digit, an odd second digit, and four different digits? (It is NOT .)
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions