Maths\Facts\Tricks\Trivia\Fun.Numbers Fun Facts

Magic 1089

Here's a cool mathematical magic trick. Write down a three-digit number whose digits are decreasing. Then reverse the digits to create a new number, and subtract this number from the original number. With the resulting number, add it to the reverse of itself. The number you will get is 1089!

For example, if you start with 532 (three digits, decreasing order), then the reverse is 235. Subtract 532-235 to get 297. Now add 297 and its reverse 792, and you will get 1089!

Presentation Suggestions:

You might ask your students to see if they can explain this magic trick using a little algebra.

The Math Behind the Fact:

If we let a, b, c denote the three digits of the original number, then the three-digit number is 100a+10b+c. The reverse is 100c+10b+a. Subtract: (100a+10b+c)-(100c+10b+a) to get 99(a-c). Since the digits were decreasing, (a-c) is at least 2 and no greater than 8, so the result must be one of 198, 297, 396, 495, 594, 693, 792, or 891. When you add any one of those numbers to the reverse of itself, you get 1089!

Mind-Reading Number Trick

Think of a number, any positive integer (but keep it small so you can do computations in your head).

1. Square it.

2. Add the result to your original number.

3. Divide by your original number.

4. Add, oh I don't know, say 17.

5. Subtract your original number.

6. Divide by 6.

The number you are thinking of now is 3!

How did I do this?

Presentation Suggestions:

Ham it up with magician's patter. Step 4 could be anything you want---someone's age, or their favorite number--- just ask the crowd for suggestions. (This will change the final outcome of Step 6, but see below for how.)

The Math Behind the Fact:

Clearly no matter what you start with, the answer should come out the same (zero wasn't allowed because of Step 3). We can see why this trick works by using a little bit of high school algebra! If you follow the instructions starting with the variable X instead of an actual number, you will see that X is eliminated by Step 5.

Using this idea, you can make up your own mental math trick right on the spot! (Just don't do anything too obvious, like tell people to add 5, subtract their original number, and say "the number you are thinking of is 5".)

Red-Black Pairs Card Trick

Here's a terrific mathematical card trick that will impress your friends. When you do this trick, the effect of the card trick will look like this:

You have a deck of cards, and you ask for a volunteer who knows how to do a riffle shuffle. You then cut the deck and then give the volunteer the halves of the deck and ask him to do one riffle shuffle and return the deck to you. Now say "There's no way I could know anything about the deck right now, right? Well, I was born with the amazing ability to feel the redness and blackness of cards with my fingertips. However, my talent is not that refined. I can only feel red and black cards in pairs." As you say this, put the deck of cards behind your back (so that you cannot see them) and then, at regular intervals, you fish around in the deck and pull out pairs of cards and show them to the audience. These pairs will all have exactly one black and one red card!

Presentation Suggestions:

Before performing the trick, order the deck alternating colors, all the way through, red-black-red-black-... etc. (When you flash the deck before their eyes, they really won't notice this pattern if you do it quickly.)

After this, there is really only one thing you need to remember to ensure that the trick works: you must cut the deck (not the spectator), and you must do it in such a way that the bottom of each half of the deck is a different color. Then, no matter how the spectator riffle shuffles the deck, the cards will always drop in red-black or black-red pairs. See below for explanation.

Then, all you have to do after the deck is returned and you put it behind your back is to pull out the top 2 cards. It will be either red-black or black-red! Then pull out the next 2 cards, which again will be red-black or black-red. You can continue in this fashion to the end of the deck, if you like!

Of course, you should make it look as if you are trying really hard to find the cards (even though what you are really doing is very easy). Spectators will wonder if you are pulling one card off the top and one card off the bottom; but you can pull the deck out and show them that this is not the case.

The Math Behind the Fact:

The reason the trick works at the point of the riffle shuffle is both simple and stunning: if you cut the deck so that the cards at the bottom of each half are different colors, then the first card that gets "dropped" in the shuffle will be a different color then the second card that gets dropped, no matter which half of the deck they come from. As an example, if the first card that gets dropped is black, then after that both halves will have red cards at the bottom, so no matter which card falls next it will be red! After this, both halves again have different colored cards at bottom and we are back to the situation at start. So all the cards will fall off in either red-black or black-red pairs.

The message of this trick is that one shuffle is not enough to randomize a deck of cards-- you really can know something about the deck after one shuffle... but only if you stack the deck in a particular way first!

Multiply 37,037 by any single number (1-9), then multiply that number by 3. Every digit in the answer will be the same as that first single number. For example: 37,037*5=185,185. 185,185*3=555,555.

If you multiply 111,111,111 by 111,111,111 you get 12,345,678,987,654,321.

Pi has been calculated to 2,260,321,363 digits. The billionth digit in Pi is 9.

Here is a simple method of telling someone their age, the trick is not difficult to do or solve but it's quick and good fun!.

1) Hand the punter a calculator (or pen & paper).

2) Mentally estimate their age but don't tell them.

3) Ask them to enter their age into the calculator (without you seeing of course).

4) Tell them that "as there are 12 months in the year, add 12 to their age".

5) Say that "as there are 7 days in a week, and 52 weeks in a year, add 752 to the number already in the calculator".

6) Ask them to tell you the last digit.

7) All you do is subtract 4 from this number and that is the last digit of their age.

8) If the number they tell you is less than 4, just add 10 before you subtract the 4 (e.g. they say 3, you add 10 then take 3 = 9).

9) You have already estimated their age so just knowing the exact last digit is usually enough to accurately be able to tell them their age.

e.g. you think they look 25.

Their sum is 23+12+752=787, they tell you 7, you take off 4 which is 3, you mentally adjust their age down to 23 (i.e. they will not look either 13 or 33 so must be 23)

Math Riddles

Which weighs more? A pound of gold or a pound of feathers?

Both weigh the same.

How is the moon like a dollar?

They both have 4 quarters.

What is alive and has only 1 foot?

A leg.

When do giraffes have 8 feet?

When there's two of them.

How many eggs can you put in an empty basket?

Only one, after that the basket is not empty.

What coin doubles in value when half is deducted?

A half dollar.

What is the difference between a new penny and an old quarter?

24 cents.

If you can buy eight eggs for 26 cents, how many can you buy for a cent and a quarter?

8.

Why should you never mention the number 288 in front of anyone?

Because it is too gross (2 x 144 - two gross).

Where can you buy a ruler that is 3 feet long?

At a yard sale.

If there were 9 cats on a bridge and one jumped over the edge, how many would be left?

None - they are copycats.

If you take three apples from five apples, how many do you have?

You have three apples.

What has 4 legs and only 1 foot?

A bed.

How many times can you subtract 6 from 30?

Once; after that it is no longer 30 (Don't try this in a test!)

If one nickel is worth five cents, how much is half of one half of a nickel worth?

$0.0125

How many 9's between 1 and 100?

20.

Which is more valuable - one pound of $10 gold coins or half a pound of $20 gold coins?

One pound is twice of half pound.

It happens once in a minute, twice in a week, and once in a year? What is it?

The letter 'e'.

How can half of 12 be 7?

Cut XII into two halves horizontally. You get VII on the top half.

When things go wrong, what can you always count on?

Your fingers.

Why are diapers like 100 dollar bills?

They need to be changed.

A street that is 40 yards long has a tree every 10 yards on both sides. How many total trees on the entire street?

10, 5 on each side.

What goes up and never comes down?

Your age.

What did one math book say to the other math book?

Wow, have I got problems!

Why is the longest human nose on record only 11 inches long?

Otherwise it would be a foot.

hope you enjoyed these math riddles.

Magic Of Maths

1 x 8 + 1 = 9

12 x 8 + 2 = 98

123 x 8 + 3 = 987

1234 x 8 + 4 = 9876

12345 x 8 + 5 = 98765

123456 x 8 + 6 = 987654

1234567 x 8 + 7 = 9876543

12345678 x 8 + 8 = 98765432

123456789 x 8 + 9 = 987654321

Some Tips and Tricks

Here are some tricks that may help you remember your times tables. Everyone thinks differently, so just ignore any tricks that don't make sense to you.

Every entry has a twin, which may be easier to remember. For example if you forget 8×5, you might remember 5×8. This way, you only have to remember half the table.

to multiply by Trick

2 add the number to itself (example 2×9 = 9+9)

5 The last digit always goes 5,0,5,0,..,

is always half of 10× (Example: 5x6 = half of 10x6 = half of 60 = 30)

is half the number times 10 (Example: 5x6 = 10x3 = ...