A professor asked John to write down any multi-digit number. But, he put a condition, the number should not end with a zero.

John put down the number 96452.

Then the professor asked John to add up the five digits and subtract the total from the original number. John did and here is what he got:

96452 – 26 = 96426

The professor then asked John to cross out any one of the five digits and tell him the remaining numbers. John crossed out the 2 and told the professor the rest of the digits. John neither told the professor the original number nor what he had done with it. Yet, the professor told John the exact number he had crossed out.

How is it possible?

The professor has to add the rest of the digits, find the nearest number to the sum that is divisible by 9 and get the difference.

So, John gave the number 9646 to the professor. The professor will add the numbers (9 + 6 + 4 + 6) to get 25. The nearest number to 25 that is divisible by 9 is 27. And the crossed out number is 27 – 25.

This is a Maths trick that relies on the power of 9.