I am a number less than 40. One of my factors is 3. The sum of my digits is 12. What number am I?

Is it 39

List the multiples of 3, ending with 39.

Yes.

To find the number, we can use the information given step by step.

First, we know the number is less than 40 and one of its factors is 3. Any number whose factor is 3 will have 3 as one of its digits, since a number is divisible by 3 if the sum of its digits is divisible by 3.

Next, we are told that the sum of the digits of the number is 12. Since 3 is one of the digits, the other digit(s) must sum up to 12 - 3 = 9.

To find the possible values of the second digit, we can list the remaining numbers whose sum is 9: 9, 8+1, 7+2, 6+3, 5+4.

However, we need to consider that the number should be less than 40. So, the only possible options left for the second digit are 9 and 6.

Now, we can combine the two digits we found with 3 to form two potential numbers: 39 and 36.

However, we are looking for a number whose factor is 3, so we need to check if either 39 or 36 is divisible by 3.

Adding the digits of 39 (3+9 = 12), we see that it is divisible by 3. Therefore, the number you are is 39.