Alex,

You are looking for a four digit number and you know that the hundreds digit is 2, so I would start there.

        2                

Now read the clues again

1. the number of tens plus the number of hundreds equals the number of thousands
   
   
2. the number of ones is half the number of tens
   
   
3. the number of ones is one more than the number of hundreds

The third clue tell you that the ones digit is one more than 2 and hence it's 3.

        2              3  

You can find the tens and thousands digits.

Penny