1. Cool Prediction Trick
A spectator randomly picks four numbers. The Maths Magician predicts the sum of the four numbers even before the trick begins!
What You Need: Paper, Pencil, Calculator
Preparation: Copy the chart below on a piece of paper on a piece of paper.
How To Perform: Tell your friend that you are going to make a prediction. Write down the following on a piece of paper without letting him see what you are writing:
The sum of the four numbers you choose will be 34!
Fold the prediction up a few times and set it aside. Hand your friend the chart you made. Tell him to circle any number on the chart. See the example below.
Next, have him cross off all of the numbers in the same column and row of the number that he circled. See below.
Now ask him to circle any number on the chart that is not circled or crossed out. After he circles his number, have him repeat the same process as before (cross off all of the numbers in the same column and row of the number that he circled.)
Then tell him to repeat these same directions until he has four numbers circled and all other numbers are crossed out. After he circled has the fourth number, there should be no more numbers to cross out.
Now, he just has one more number left to circle and then we are ready for the grand finale!
Have him add together the four numbers that are circled and announce the total to you. Next unfold the paper that was placed aside to reveal the prediction. It will always match his total!
Secret: Let’s see why this trick works. Anytime you have a square array of consecutive numbers, the sum of the four circled numbers will always be the sum of either of the diagonals.
So, for our example above, the numbers for one of the diagonals is 1, 6, 11 and 16. Let’s add these numbers up:
1 + 6 + 11 + 16 = 34
The numbers for the other diagonal are 4, 7, 10, and 13. Adding these gives:
4 + 7 + 10 + 13 = 34
So, there’s really no need to add up both diagonals.
If your friend wants you to repeat the trick
Usually, people want to see a trick more than once. So the second time I perform the trick, I use a different number chart so that the prediction number may not be the same. The number chart below can be used to perform the trick a second time.
The prediction sum for this set of numbers will be 65. Just add up either diagonal and the sum is 65. And there you have it, another cool maths trick to amaze friends and family!
2. Calendar Mathematical Trick
This calendar maths trick is yet another amazing maths activity that lets kids (and adults) see just how cool maths is! Just grab a calendar or wherever you can get one.
The Effect:
❑ Have a friend circle a group of nine numbers. Make sure the numbers are in a 3 by 3 rectangle like the picture shows here.
❑ Tell your friend that you have the special ability to add all nine of the numbers circled in your head in a matter of seconds!
❑ You give the correct answer and have him check it with a calculator.
The Secret: All you have to do to get the sum of all nine numbers is to multiply the number in the centre of the circled numbers by nine! So for our example, the centre number is 11.
So, you just need to multiply in your head,
“9 x 11”.
For those of you who’ve memorized your multiplication facts, you know right away that the answer is 99.
HANDY TIP: To multiply by 9 quickly, just multiply by 10 and then subtract your number. So to get 22 x 9 you multiply 22 x 10 =220 (easy!) and then subtract 22. With a bit of practice you can do this quickly in your head.
After you have performed the trick once, perform it again, this time make it a little more interesting. Challenge them to a race. Say to your friend, “I will add the nine numbers in my head while you add them with the calculator, and I will get the answer first”. You just perform it the same way as before—just multiply the middle number by 9 to get the answer.
He should be pretty impressed and if he is are like most, will wonder how it was done. Usually no one will figure out the secret.
Now, how about a grand finale to impress him even more. This time tell him to circle 20 numbers in a 5 by 4 rectangle—and you will add up all the circled numbers in your head in a couple of seconds!
Take a look a the picture below.
The Secret: Add the smallest and largest numbers that are circled and multiply their sum by 10. And that’s it. Pretty cool, huh.
So for the above example,
6 + 31 = 37 and then,
37 x 10 = 370
So the sum of all 20 numbers is 370!
Have fun with this trick. No one will be able to figure out how you get the answer so fast!
3. Mathematical Magic Tricks
Not only are maths magic tricks a fun way to amaze friends, but they can also help kids build some mathematical skills along the way! In this maths trick, the math magician performs an instant calculation by quickly giving the sum of any four numbers a volunteer covers up!
The first thing you need to know before I show you the trick is the square that you see on this page is special. It’s actually called a magic square. No kidding……Do you know why it’s called a magic square? Notice what happens if you add up all the numbers in the top row.
24 + 11 + 3 + 20 + 7 = 65
Now take a look at the second row.
5 + 17 + 9 + 21 + 13 = 65
Can you guess what the numbers in the third row add up to? If you guessed 65, you’re right. But there’s more……. The numbers in the first column add up to 65 as well.
24 + 5 + 6 + 12 + 18 = 65
And the other two columns also add up to 65. And the two diagonals also add up to 65. So that’s why it’s called a magic square. 65 is the magic number. Now back to our maths magic trick.
Performing the Trick:
First you need to know what the magic number is for the square you are using. For the square shown on this page, I already explained to you that the magic number is 65.
Next, you figure out what number to subtract from 65 after the volunteer has covered up any four numbers.
I’ll show you how to find the number to subtract from 65 with a few examples. Look at the first example below. Here you can see someone covered up four numbers at random with the green square.
As soon as they cover up four numbers with a square, in your mind you will extend a diagonal line, two numbers get past the outside corner of the covered square. In order to go over two numbers past the outside corner of the covered square, you can only go in one direction.
If you try to go diagonally in any other direction, you will not be able to go two numbers over. Take a look at the picture below. Notice that you can only extend the line two numbers in one direction. The number you arrive at is 8.
This is the number that you subtract from 65.
65—8 = 57
So the numbers that are covered add up to 57.
Look back at the top picture and check for yourself to see that the numbers that are covered up, when added together are 24 +11 + 5 + 17 = 57!
And there you have it…..
Have fun with it!
4. Pick Pocket Mathematical Number Trick
This Pick Pocket Math Number Trick helps kids get practice with addition, subtraction and multiplication—all in one shot!
Really impress friends and family by correctly guessing the amount of change they have in their pockets!
What You Need:
Find a volunteer to work your maths magic on.
Make sure your volunteer has some change in his pocket. But he does not reveal it to you..
Paper
Pencil
What To Do:
Have your volunteer multiply his age by two.
Then he will add five.
Now multiply the previous sum by fifty.
Subtract 365.
Add the amount of pocket change, but do not count any change that is over $1.
Add 115.
Notice that the first two digits will be the person’s age, and the last two digits are the amount of the person’s pocket change.
Pretty Cool Stuff!
5. Math Magic Trick
Here’s a really cool Math Magic Trick that kids can use to impress family and friends and build basic mathematical skills too!
Materials: 5 dice
Performing the Trick:
1. Tell the spectator that you can see through the dice all the way to the bottom numbers.
2. Roll all 5 dice on the table.
3. Pretend that you are looking through the dice to see the bottom numbers. (What you are actually doing is adding up the top numbers of all 5 dice.)
4. Then you will announce the sum of the bottom numbers. (All you have to do is subtract the sum of the numbers you added in your mind from the top from 35.)
5. Then turn over the 5 dice and have the spectator add the numbers of top numbers. They will be amazed at how you did it!
How the Trick works:
On any die, the sum of the top number and the bottom number is 7. So for example, if you toss one die and the top number of the die is a 3, the number at the bottom of the die will be a 4, since 4 + 3 = 7.
So if you throw out 5 dice, the total of all the top and bottom numbers will be:
5 x 7 = 35
