Everyone knows magic tricks are fun, but not many people realize that math is just as much fun as magic. Whether you're teaching students or playing with friends, these tricks will surprise them.
Step
Method 1 of 2: Guessing Age and Shoe Size
Step 1. Ask a volunteer to write down her age
Give him a piece of paper and instruct him to show you the numbers he wrote down.
This trick won't work for people 100 years of age or older, but it almost never does
Step 2. Have him multiply the number by 5
Have him complete the calculations according to your instructions. Start by asking him to multiply his age by 5.
- For example, if he was 42 years old, he would write 42 x 5 = 210.
- He can calculate using a calculator if he wants.
Step 3. Write a zero at the end of the answer
This is the same as multiplying a number by 10, but having volunteers follow this multiplication trick is more difficult for them.
In this example, adding zero to 210 results in 2100.
Step 4. Add today's date
Which number to add doesn't really matter - we can change the numbers later - but today's date is a small number that's easy to add. Say the date out loud to make sure he knows it.
- For example, if today is March 15, the volunteer will add up 2100 + 15 = 2115.
- Ask him to ignore the month and year.
Step 5. Duplicate the answer
The volunteer must multiply the answer by two. (Calculators are very useful at a stage like this.)
2115 x 2 = 4230.
Step 6. Add the volunteer's shoe size
Ask the volunteer to write down his shoe size, and round it off if the number is not an integer. He had to add this number in his final answer.
If her shoe size is 7, she will add 4230 + 7 = 4237.
Step 7. Subtract the number by twice today's date
Calculate the multiplication of this date in your mind, then tell him to subtract the number from your calculation.
For example, today is March 15th, so multiply 15 x 2 = 30 in your head. Say "Subtract your answer by 30" and the volunteer will calculate 4237 - 30 = 4207.
Step 8. Uncover the magic
Tell him to read the answer aloud. The first part of the number is his age, and the last two digits are his shoe size.
Method 2 of 2: 1089. Trick
Step 1. Choose a friend who is quite good at math
This trick only involves adding and subtracting, but some people can get dizzy with the instructions given. This trick works best in the presence of friends who will pay close attention to you, and are less likely to miscalculate.
Step 2. Write 1089 on a hidden piece of paper
Announce that you are going to write a "magic number" on a piece of paper. Write 1089 without telling anyone, then fold the paper in half.
Step 3. Ask your friend to write down a number with three different digits
Tell him not to tell or show you the number. Make sure he understands that each digit written cannot be the same.
- For example, he chose a number 481.
- He may also need a calculator.
Step 4. Instruct to write the numbers in reverse order
In the line below the initial number that has been selected, he must write the same number but in reverse order.
For example, the reciprocal of 481 is 184.
Step 5. Make it a subtraction problem
Once your volunteer has two numbers, ask him to subtract the larger number from the smaller number.
481 - 184 = 297.
Step 6. If the number is only two digits, add leading zeros
Now ask him if the subtraction number is two or three digits long, without telling you the exact number. If the number consists of only two digits, ask him to put a leading zero.
In this example, 297 is three digits long, so you can skip this step. Sometimes there are subtractions of 99, and this step will change that number to "099."
Step 7. Invert this number
Ask him to write the answers in reverse order. If he adds a leading zero, remind him to include the zero as a part.
For example, the reciprocal of 297 is 792.
Step 8. Add the final result and the reverse
As a final calculation, ask your friend to add the last two numbers he wrote down.
In this example, 792 + 297 = 1089.
Step 9. Show everyone your predictions
Say that you know the last number he wrote down. Unfold the paper and reveal the 1089 that was written earlier.
The answer is always 1089. If your friend's answer is different, he's either not following the instructions or he's miscalculated
Tips
- Do not repeat this trick in front of the same group of people. For example, guessing 1089 a second time is less impressive!
- The 1089 trick actually works with most three-digit numbers, even if the two digits are repeated. This trick doesn't work with palindrome numbers (like 161 or 282). Asking for three different digits is an easy way to avoid failing this trick.
- Don't repeat this trick in front of the same people! If you do, he'll quickly notice the trick and will purposely mess it up when you do it in front of other people and make it look like you're the flop. This can be very embarrassing, especially when you do it at a party or a crowd.
