Maths tricks

Cool Math Tricks

A spectator randomly picks four numbers.The Math 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 them 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 them to circle any number on the chart. See example below.

Next have then cross off all of the numbers in the same column and row of the
number that they circled. See below.

Now ask them to circle any number on the chart that is not circled or crossed
out. After they circle their number, have them repeat the same process as
before (cross off all of the numbers in the same column and row of the number
that they circled.)

Then tell them to repeat these same directions until they have four numbers
circled and all other numbers are crossed out. After they circle the fourth
number, there should be no more numbers to cross out.

Now they just have one more number left to circle and then we are ready for
the grand finale!

Have them 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 their 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 the prediction number will 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 math trick to amaze friends
and family!

Calculator Tricks

You'll find lots of cool Calculator tricks on this page that will amaze friends and
family. Another way to get students to see how fun and cool math really is!
Grab your calculator if you haven't yet, and let's Get Ready....Set....Calculate....

"Got Your Number" Calculator Trick

Have someone type in any number between 1 and 900 into the calculator without
letting you know what it is. (Actually, this trick will work for numbers greater than
900, but on most calculators the resulting display will not be large enough). Also
tell them to choose a number with mixed digits and it should be a positivenumber.
Next, you will have them perform the following calculations......on the calculator of
course (:

1. Multiply their number by 3.
2. Then multiply the result by 7.
3. Then multiply the result by 37.
4. Then multiply the result by 11.
5. Finally multiply the result by 13.
Now ask them to show you the number showing in the calculator.
Ok, now here's the magic! By looking at this number, you will be able to reveal
the number they started with. For example, let's say the random three digit number
they first entered into the calculator was 763. After performing all f the
multiplications that you tell, they would end up with 84777693 on the display.

So, are you wondering how you come up with their starting number of 763? Good, I thought
you might want to know. I'm going to explain below and with a little practice you'll be

performing this trick in no time like a true "Mathemagician!"

Here's How It Works.....

We start the trick by multiplying by 3, 7, 37, 11, and 13. But guess what...

3 x 7 x 37 x 11 x 13 = 111,111

So really, we are just having the person multiply their original number by 111,111.

Depending on what three digit number they choose at the start of the trick, their final
number will appear in one of the following formats below. Don't worry, I'll explain. I'm going
to do a few examples.

HSSSSSV
HSSSSVF
HHSSSVVF

H = "Head" - It will consist of one, or two, or no digits.

S = "Stem" - It will consist of easily identifiable REPEATING digits, always located in the
center.

V = "Variable" - It will consist of one, or two, or no digits.

F = "Final" - It will always consist of a single digit.

Just hang with me, it's not that bad... I'm going to do a few examples so you can see exactly
what's going on, okay...

After you memorize the format above, here's what to do next.

1. Subtract the "variable" V or VV from the SAME number of digits in the
"stem".

2. Subtract the difference obtained in step 1 from the entire "head" H or HH.
3. Attach the final digit to the difference you obtained in step 2. This is the

number your friend used!

Example 1: Your friend chooses the number 257.

After you get your friend to goes through all of the multiplications on the
calculator, their final result for this example will be 28555527.

Head: 28
Stem: 5555
Variable: 2
Final: 7

Step 1: 5 - 2 = 3
Step 2: 28 - 3 = 25
Step 3: Attach 25 to 7 to get 257.

Example 2: Your friend chooses the number 632.

After you get your friend to goes through all of the multiplications on the calculator, their
final result for this example will be 70222152.

Head: 70
Stem: 222
Variable: 15
Final: 2
Step 1: 22 - 15 = 7
Step 2: 70 - 7 = 63
Step 3: Attach 63 to 2 to get 632.

Calendar Math Trick

This calendar math trick is yet another amazing math activity that lets kids
(and adults) see just how cool math is! Just grab a calendar from off the wall
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 them check it with a calculator.
The Secret: All you have to do to get the sum of all nine numbers is
tomultiply the number in the center of the circled numbers by nine! So for
our example, the center 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 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 perform 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.
They should be pretty impressed and if they 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 them even more. This time tell
them 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.

29

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! If you liked this calendar math trick, we will be adding
another real soon that is also really cool.

Math Magic Tricks

Not only are math magic tricks a fun way to amaze friends, they can also help kids build

some math skills along the way! In this math trick, the math magicianperforms an
instant calculation by quickly giving the sum of any four numbers a volunteer

covers up!

134

Are you ready? Great, Let's go.........
Print the magic square.
Ok, you printed the magic square, right. Good! 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 amagic 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 also.

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 math 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
themagic number is 65.

 Next, you figure out what number to subtract from 65 after the volunteer covers
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 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.

134

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!

You can also find out more about magic square puzzles here.

We have found this fun math tricks on this
page:
http://www.learn-with-math-games.com/