A Mind Boggling Numbers Game

Do you love numbers? How about guessing games? Well, if you do, I'm sure you will like this simple yet tricky game that I want to share. 

Anyway, this guessing game involving numbers best suits the teachers. This can be done in class when the students seem bored or tired.  I used this simple, exciting yet mind boggling trick to my Korean students before. But anybody can also enjoy this.

Here we go! If you are a teacher, ask your students to think of any number they want (at least 3 digits). It would be better if they write it down since they'll be dealing with some mathematical operations later on. Remind your students that the number they want should not be disclosed to you. Next, tell them to add all the digits of the number they chose. After that, ask them to subtract the total from the original number. Don't worry if you're quite lost. I will wrap this up later. Now, after subtracting, ask your students to hide one digit from the difference, then tell you the remaining numbers. What's the catch? You are going to guess the hidden number. Do you have any idea how to do it?

Again, here's the procedure.

1. Ask each student (or anyone interested) to think of a number (at least 3 digits). example: 12345
2. Then, let him/her add all the digits. 1+2+3+4+5=15
3. Subtract the total from the original number. 12345-15=12330
4. After that, ask your student to hide any digit, then give you the remaining numbers.

The student can also jumble the numbers before giving them to you. Take for example, the hidden number is 2. Your student will give you 3301. Of course, the hidden number is 2, but how would you know it?

It's very simple. Just make sure you memorize the multiples of 9 (9,18,27,36,45...). What you're going to do is add all the digits given by your student. 3+3+0+1=7. Since 7 is lesser than 9, all you need is to know the  difference. The difference is 2, therefore, that is the hidden number.

If the total exceeds 9, then go to the next multiple. 

Now, what if the total is 9, 18 or 27? There are two possible answers. It could either be 0 or 9, but just give one answer. If the student says wrong, just make an alibi by saying, "Oh, I'm sorry. It's 9." If the student still says it's wrong, better ask him to review the procedures.

Using a calculator, this trick or puzzle can also be done. Type any number then multiply it by 9, 99 or 999. After that, hide one digit. The same procedure is applied. 

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