take your pick ...
345 , 354 , 363 , 372 , 381 , 390
the sum of all the digits is 12.
what is the mystery number?
345 , 354 , 363 , 372 , 381 , 390
so 3 + x + y = 12
x+y = 9
and the lead digit has to be 3, so possible cases
345
354
363
372
381
390
Was there more information given?
Look at the first of the "Similar Questions" below.
Let's start by looking at the hundreds digit. Since the number is between 337 and 400, the hundreds digit can only be 3.
Next, let's look at the tens digit. The sum of all the digits is 12, and we already know that the hundreds digit is 3. This means that the sum of the tens digit and the units digit must be 9 (12 - 3 = 9).
We want the number to be as close to 337 as possible, so we can start with the largest possible tens digit, which is 8 (9 - 1 = 8).
Now, we know that the hundreds digit is 3, the tens digit is 8, and the sum of all the digits is 12. Therefore, the units digit must be 1 (12 - 3 - 8 = 1).
Therefore, the mystery number is 381.