In that case pick a three-digit number. The digits of the number must be different from each other. That is important. For demonstration purposes let's say you picked 123.
Next you want to reverse your three-digit number. 123 would become 321. Keep both numbers though, 123 and 321.
Next subtract the lesser number from the greater number. For our demonstration it will be 321 - 123. Find your answer, which, if you used 123, will be 198.
Now, take the answer from your subtraction - 198 - and reverse THAT. (198 becomes 891.) Keep both numbers.
Now, add the two numbers together. (I.e. 198 + 891.)
So I'm gonna predict your answer now...is is 1089? I thought so. If it isn't then you must have done it wrong. That's okay, this is probably why:
If you got 198 as opposed to 1089 I'll help you out, it's a common mistake. Let's say you picked a three-digit number such as 546. Your problem would be 645 - 546 (= 99), then 99 + 99 = 198. But if you say that "ninety-nine" is 099 instead of just 99, you'll get 990-099 (= 891), then 891 + 198 = 1089! Simple.
So what do you think? Cool huh? Did it work for you?