Question

How many different positive integers divisible by 4 can be formed using each of the digits 1, 2, 3, and 4 at most once, and no other digits

Answer 1

For a number to be divisible by 4, its last two digits must form a number divisible by 4. Using the given digits, we can create the following such numbers: 12, 24 and 32. For each such number, there are 2 ways to select the remaining two digits. Therefore, there are
`3\cdot2=6` such integers.