1. That’s Original
Ask someone to write down any four-digit number. When they have done that, tell him that he has selected a very magical number. Explain the reason which is as follows:
1. Write down the number. (4829)
2. Write down the first digit. (4)
3. Write down the first two digits. (48)
4. Write down the first three digits. (482)
5. Add these together. (4 + 48 + 482 = 534)
6. Multiply this answer by 9. (534×9 = 4806)
7. Add up the original four digits. (4 + 8 + 2 + 9 = 23)
8. Add these last two results. (4806 + 23 = 4829)
Following this process means the original number will always appear at the end!
2. The Number 11 Sandwich
A very neat trick for multiplying a two-digit number by 11 is to write down the number you are multiplying by, leaving a space between the two numbers. For example, to work out 35×11, leave a space between the 3 and 5 = 3_5. Now, add these two digits and place the answer in between. So 3 + 5 = 8, then place the 8 in between the 3 and 5 to make 385. Check this on a calculator to see that 35×11 is 385.
This method works if the total of the two digits is less than ten. If they add up to ten or more, you will need to add the 1 to the first digit and place just the second number in the space. For example, to do 67×11 you would separate the 6 and 7, add 6 and 7 to make 13, but rather than place 13 in between, place the 3 in the space and add the 1 to the 6, so the answer is 737.
3. Money Mathematical Magic Trick
Materials:
Paper
A rupee note
Pen or pencil for writing
1. Ask someone in the group for a rupee note
2. Ask a child to write down the first 5 numbers of the serial number of the note.
For Example: 5 6 7 8 9
3. Ask another child (or the same child) to rearrange the numbers in a different number.
For Example: 7 9 6 5 8
4. Now, put the largest number on top and subtract the two numbers.
For Example:
79658
- 56789
22869
5. With this new number, you can have some fun now. Ideally, one of the presenters can do all of this with the children while the other presenter walks away so that the other presenter may not hear or see any of the previous steps. When you’ve completed step 4, you can bring the other presenter back to the group. Still, don’t show the results. Ask one of the children to remove one of the numbers from the answer except for the number 9. Tell the child to tell the other presenter the new number. For example, let’s pick the number 8. So now, the new number is: 2269
6. The other presenter can tell the child what number is missing using something called digital roots. We will take the remaining new number and add each digit together.
For example: 2 + 2 + 6 + 9 = 19; now, we will take this answer and add its digits together until we have a one-digit answer. Now, 19—1 + 9 = 10; 10—1 + 0 = 1. The digital root is 1. Now, we will take this digital root and subtract it from 9: 9—1 = 8 (that’s the missing number). This works every time except for the number 9. If the child picks a 9 or 0, both answers result in 0. This works because we have a base 10 number system.
