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# Amazing Maths Trick

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I just revised this powerpoint, taking out the one trick that was not appropriate for classroom use.
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### Amazing Maths Trick

1. 1. Amazing Math Trick 234X234+1234-875=??? Trick! Trick!
2. 2. The 7-11-13 trick! <ul><li>This trick makes you look like your brain is a mega fast calculator! </li></ul><ul><li>Ask a friend to write down ANY three digit number such as 231 or 884. Ask them to multiply the number by </li></ul><ul><li>x 7 x 11 x 13 </li></ul><ul><li>...but even if your friend has used a calculator, you will have written down the answer ages ago! It's fiendish! </li></ul><ul><li>THE SECRET: all you do is write out the starting number twice! So 231 will become 231231 and 884 will become 884884. You don't believe it? Well try it on this calculator and see for yourself! You work this calculator by clicking the mouse on the buttons. Go on, put in ANY three digit number then x7 x11 x 13 and see what you get! </li></ul>
3. 3. The 3367 trick: <ul><li>This trick is similar to the 7-11-13 trick. It's harder to do, but it looks far more miraculous! </li></ul><ul><li>Get a friend to pick any 2 digit number e.g. 74 </li></ul><ul><li>x 3367 </li></ul><ul><li>To work out the final answer you have to imagine the original number written out three times e.g. 747474 then divide it by three. 249158 </li></ul><ul><li>This one takes practice, but unlike the others, it's very hard to see how it's done! </li></ul>
6. 6. The &quot;24&quot; Mystery! <ul><li>A Murderous Math fan called OBAID pointed out that if you square ANY prime number bigger then 3, then subtract 1, the answer always divides by 24! E.g. 112 = 121 then 121 - 1 = 120 and yes 120 does divide by 24. </li></ul><ul><li>WHY? </li></ul><ul><li>If you understand algebra, (and you've read The Phantom X ) then you'll know that all prime numbers can be written as (6n+1) or (6n-1). </li></ul><ul><li>(6n+1)2 = 36n+12n+1. So (6n+1)2 -1 = 36n+12n. This factories to 12n(3n+1). Either n or (3n+1) must be even, therefore the whole expression must be divisible by 24. </li></ul><ul><li>(6n-1)2 = 36n-12n+1. So (6n-1)2 -1 = 36n-12n. This factories to 12n(3n-1). Either n or (3n-1) must be even, therefore the whole expression must be divisible by 24. </li></ul>
7. 7. The Prime Number Trick <ul><li>Using prime numbers, you can amaze your friends with a prime prediction... </li></ul><ul><li>Ask your friends to pick any prime number bigger than 5, but they must not tell you what it is. </li></ul><ul><li>Square it. (In other words multiply the prime number by itself.) </li></ul><ul><li>Add 17 </li></ul><ul><li>Divide by 12 </li></ul><ul><li>Without knowing which prime number your friends picked, you can still tell them: There will be a remainder of 6. </li></ul><ul><li>For example, if you want to try the trick with the prime number 2801, here's what to push: </li></ul><ul><li>2801 * 2801 = + 17 = / 12 = </li></ul><ul><li>...and that's the answer! Now find a new prime number and try it. </li></ul>
9. 9. Phone Number Trick <ul><li>Here is a math trick so unbelievable that it will stump you. Personally I would like to know who came up with this and why that person is not running the country. 1. Grab a calculator. (you won't be able to do this one in your head) 2. Key in the first three digits of your phone number (NOT the area code) 3. Multiply by 80 4. Add 1 5. Multiply by 250 6. Add the last 4 digits of your phone number 7. Add the last 4 digits of your phone number again. 8. Subtract 250 9. Divide number by 2 Do you recognize the answer ?????? </li></ul>
10. 10. Joker’s Math Trick 1 <ul><li>complete this amazing Math Trick just follow the instruction below and complete the steps. You'll be surprised with the results! All you'll need is a pen or pencil and some paper! </li></ul><ul><li>Pick a number between 1 and 100. </li></ul><ul><li>Multiply it by 5. </li></ul><ul><li>Add your age minus the number in family. </li></ul><ul><li>Divide the number by 10 rounding to the nearest decimal. </li></ul><ul><li>Write down the number on one side of a piece of paper. </li></ul><ul><li>Pick another different number between 1 and 100. . </li></ul><ul><li>Multiply by 1998. </li></ul><ul><li>Add the number in your family and subtract your age. </li></ul><ul><li>Divide the number by 10 rounding to the nearest decimal. </li></ul><ul><li>Write down the number on the other side of the piece of paper. </li></ul>
11. 11. Joker’s Math Trick 2 <ul><li>Take the first 2 digits of your home phone number and add them to the last 2 digits of your phone number. </li></ul><ul><li>Multiply by 365. </li></ul><ul><li>Write the number on a new sheet of paper. </li></ul><ul><li>Fold the first page in half. </li></ul><ul><li>Now fold the second page. </li></ul><ul><li>Place them side by side. </li></ul><ul><li>Now pick up the two sheets - sheet one in your left hand and sheet two in your right hand. </li></ul><ul><li>Find a bin/drawer and place the sheets in it. </li></ul><ul><li>Now using both your hands... </li></ul><ul><li>Slap yourself around the head while repeating: &quot;I'm a stupid person who wastes too much time on junk like this.&quot; </li></ul>
12. 12. 5 squared shortcut Trick 1 <ul><li>Here is a really quick way to square any number with a 5 on the end Lets take </li></ul><ul><li>  </li></ul><ul><li>Ok, so what you have to do is split up the numbers, giving you </li></ul><ul><li>and    </li></ul><ul><li>Forget about the for the moment and do this: </li></ul><ul><li>Always add 1, adding 1 to the 4, so we get 4 + 1 = 5 </li></ul><ul><li>Then multiply this answer, 5, by the original first number, 4 </li></ul><ul><li>5 X 4 = 20 </li></ul><ul><li>So what you have is 20 and </li></ul><ul><li>Everyone knows = 25 right? Well it does. This is what makes it easy. </li></ul><ul><li>Put the two answers together and that's the answer! </li></ul><ul><li>2025 </li></ul>
13. 13. 5 squared shortcut Trick 2 <ul><li>This works for any number ending in but when the numbers get over 100 it tends to get a little trickier with the multiplication. </li></ul><ul><li>Give it a try with another number. </li></ul><ul><li>Try , it isn't difficult. </li></ul><ul><li>Split the numbers apart: </li></ul><ul><li>8 and </li></ul><ul><li>Again, forget about the </li></ul><ul><li>Add 1 to 8  </li></ul><ul><li>8 + 1 = 9 </li></ul><ul><li>Multiply 9 by the first number, which was 8 </li></ul><ul><li>9 X 8 =72 </li></ul><ul><li>Now, put all the numbers together, 72 and </li></ul><ul><li>  = 25 </li></ul>
14. 14. Squaring a 2-digit number beginning with 5 <ul><li>Take a 2-digit number beginning with 5. </li></ul><ul><li>Square the first digit. </li></ul><ul><li>Add this number to the second number to find the first part of the answer. </li></ul><ul><li>Square the second digit: this is the last part of the answer. </li></ul><ul><li>    Example: </li></ul><ul><li>If the number is 58 , multiply 5 × 5 = 25 (square the first digit). </li></ul><ul><li>25 + 8 = 33 (25 plus second digit). </li></ul><ul><li>The first part of the answer is 33   3 3 _ _ </li></ul><ul><li>8 × 8 = 64 (square second digit). </li></ul><ul><li>The last part of the answer is 64    _ _ 6 4 </li></ul><ul><li>So 58 × 58 = 3364 . </li></ul><ul><li>    See the pattern? </li></ul><ul><li>For 53 × 53, multiply 5 × 5 = 25 (square the first digit). </li></ul><ul><li>25 + 3 = 28 (25 plus second digit). </li></ul><ul><li>The first part of the answer is 28   2 8 _ _ </li></ul><ul><li>3 × 3 = 9 (square second digit). </li></ul><ul><li>The last part of the answer is 09    _ _ 0 9 </li></ul><ul><li>So 53 × 53 = 2809 . </li></ul>
15. 15. Squaring a 2-digit number ending in 5 <ul><li>Choose a 2-digit number ending in 5. </li></ul><ul><li>Multiply the first digit by the next consecutive number. </li></ul><ul><li>The product is the first two digits: XX _ _. </li></ul><ul><li>The last part of the answer is always 25: _ _ 2 5. </li></ul><ul><li>    Example: </li></ul><ul><li>If the number is 35 , 3 × 4 = 12 (first digit times next number). 1 2 _ _ </li></ul><ul><li>The last part of the answer is always 25: _ _ 2 5. </li></ul><ul><li>So 35 × 35 = 1225 . </li></ul><ul><li>    See the pattern? </li></ul><ul><li>For 65 × 65, 6 × 7 = 42 (first digit times next number): 4 2 _ _. </li></ul><ul><li>The last part of the answer is always 25: _ _ 2 5. </li></ul><ul><li>So 65 × 65 = 4225 . </li></ul>
16. 16. Squaring numbers made up of sixes <ul><li>Choose a a number made up of sixes. </li></ul><ul><li>The square is made up of: </li></ul><ul><ul><li>one fewer 4 than there are repeating 6's </li></ul></ul><ul><ul><li>3 </li></ul></ul><ul><ul><li>same number of 5's as 4's </li></ul></ul><ul><ul><li>6 </li></ul></ul><ul><li>    Example: </li></ul><ul><li>If the number to be squared is 666 </li></ul><ul><li>The square of the number has:  4's (one less than digits      in number)           4 4  3                             3  5's (same number as 4's)        5 5  6                                   6 </li></ul><ul><li>So 666 × 3666333 = 443556 . </li></ul><ul><li>    See the pattern? </li></ul><ul><li>If the number to be squared is 66666 </li></ul><ul><li>The square of the number has:  4's (one less than digits       in number)           4 4 4 4  3                                 3  5's (same number as 4's)            5 5 5 5  6                                           6 </li></ul><ul><li>So 66666 × 66666 = 4444355556 . </li></ul>