Science Fun: Einstein's Puzzle

Einstein's puzzle

You'll need a friend, a calculator, a piece of paper and a pen for this one.

1. 1. Without letting your friend see, write the number 1089
       on a piece of paper.
2. 2. Fold the piece of paper and hand it to a friend for
       safekeeping. It shouldn't be read until the end of the puzzle.
3. 3. Ask your friend to write down any three-digit number
       without letting you see it. The first and last digits must
       differ by at least two.
4. 4. Ask your friend to reverse the number,
       and then subtract the smaller from the larger
       (e.g., 654 - 456 = 198).
5. 5. Now, with their number still hidden from you, tell your
       friend to reverse the new number (e.g., 198 becomes 891).