What is the smallest five-digit number divisible by 4 that can be formed with the digits 1, 2, 3, 4, and 9?
A number is only divisible by 4 if the number formed by its last two digits is divisible by 4. Thus, using only the digits 1, 2, 3, 4, and 9, the only possibilities are 12, 24, 32, or 92. Since 9 is the largest digit, we should place it "as far to the right as possible," meaning that 9 must be the digit in the tens place, i.e., our number ends with 92. The other digits 1, 3, and 4 must appear in descending order to the left of 92, i.e., the first three digits of the number should be 134. Therefore, the number we are looking for is 13492.