You will require paper and pencils, or calculators for this activity.
Write the number 1089 on a piece of paper and tape it backwards to the blackboard.
Ask everyone in the class to -
1) Write down a three-digit number whose first and last digits differ by at least two.
2) Reverse the digits in the above number and subtract the smaller number from the larger.
3) Now, Reverse the digits in the above answer, and add the answer and its reverse.
4) The final result will always be exactly 1089 !
Now show the class that you wrote that answer on that paper on the blackboard.
For Example :
Assume you choose the number 431.
Its reverse is 134. And 431 - 134 = 297.
The reverse of 297 is 792. And 297 + 792 = 1089.