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  #1  
Old 04-23-07, 04:57 PM
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Amusing math trick.

Grab a calculator. (you won't be able to do this one in your Head)

1. Key in the first three digits of your phone number (NOT the Area code)
2. Multiply by 80
3. Add 1
4. Multiply by 250
5. Add the last 4 digits of your phone number
6. Add the last 4 digits of your phone number again.
7. Subtract 250
8. Divide number by 2

Do you recognize the answer ??
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  #2  
Old 04-23-07, 05:12 PM
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What do you mean I can't do that in my head? Speak for yourself.
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  #3  
Old 04-23-07, 06:27 PM
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Originally Posted by ATH View Post
What do you mean I can't do that in my head? Speak for yourself.
Sorry jeenyus.
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Old 04-23-07, 06:29 PM
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thats cool!
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Old 04-24-07, 04:07 AM
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Quote:
Originally Posted by StrangeCheez View Post
Grab a calculator. (you won't be able to do this one in your Head)

1. Key in the first three digits of your phone number (NOT the Area code)
2. Multiply by 80
3. Add 1
4. Multiply by 250
5. Add the last 4 digits of your phone number
6. Add the last 4 digits of your phone number again.
7. Subtract 250
8. Divide number by 2

Do you recognize the answer ??
if your phone number is abcdefg for some digits {a,b,c,d,e,f,g}, the equation comes out to:

(((80*abc + 1)*250)+2*defg-250)/2
= (80*250*abc + 250 +2*defg-250)/2
= (20000*abc +2*defg)/2
= 10000*abc + defg
= abc * 10^4 + defg
= abc0000 + defg
= abcdefg
= your phone number

There's nothing interesting about this. A gradeschooler could invent the steps to get this result, as it's all based on (80 *250)/2 = 10000.
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Old 04-24-07, 10:02 AM
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Quote:
Originally Posted by baseline bum View Post
if your phone number is abcdefg for some digits {a,b,c,d,e,f,g}, the equation comes out to:

(((80*abc + 1)*250)+2*defg-250)/2
= (80*250*abc + 250 +2*defg-250)/2
= (20000*abc +2*defg)/2
= 10000*abc + defg
= abc * 10^4 + defg
= abc0000 + defg
= abcdefg
= your phone number

There's nothing interesting about this. A gradeschooler could invent the steps to get this result, as it's all based on (80 *250)/2 = 10000.
I said amusing. I didn't imply that it was some life changing, supremely difficult math problem. It is pointless, and it is easy, but I have not seen it before and was amused. Sorry if you found that it was beneath you.
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Old 04-24-07, 11:25 AM
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Would punching 58,008 into your calculator and then turning it upside down qualify as a math trick?
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Old 04-24-07, 11:28 AM
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Originally Posted by coyotes_geek View Post
Would punching 58,008 into your calculator and then turning it upside down qualify as a math trick?
I asked my wife. She hit me!!
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Old 04-24-07, 11:28 AM
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Originally Posted by coyotes_geek View Post
Would punching 58,008 into your calculator and then turning it upside down qualify as a math trick?
Yes. That's a classic from waaay back in the day.
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Old 04-24-07, 02:54 PM
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If you take a convolution integral, you can LaPlace transform the arguments, add them together, and inverse LaPlace transform them, and the result is the product of the convolution arguments.

Now that's a sweet math trick.

$
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Old 04-24-07, 03:15 PM
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My favorite math trick so far is either using the heat equation to value a future option or using modular arithmetic on large numbers to encode a message into an uncrackable code (RSA).
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Old 04-24-07, 03:34 PM
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Pointing out to mav fans that 3 > 0 is another math trick I find quite entertaining.

Quote:
Originally Posted by StrangeCheez View Post
Yes. That's a classic from waaay back in the day.
Yep. Give any puberty stricken teenage boy a calculator and he'll have derived that magic numerical sequence in a matter of minutes.
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Old 04-24-07, 03:46 PM
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Quote:
Originally Posted by bonnington View Post
Exactly, I did the same thing.
But I did it in my head

Quote:
Originally Posted by SupermanThree View Post
I asked my wife. She hit me!!
Good for her! Men truly are from Mars.
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Old 04-24-07, 08:12 PM
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Quote:
Originally Posted by StrangeCheez View Post
I said amusing. I didn't imply that it was some life changing, supremely difficult math problem. It is pointless, and it is easy, but I have not seen it before and was amused. Sorry if you found that it was beneath you.
Maybe you should have them type in 7734206 instead.
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Old 04-24-07, 08:44 PM
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Quote:
Originally Posted by Money4Nothing View Post
If you take a convolution integral, you can LaPlace transform the arguments, add them together, and inverse LaPlace transform them, and the result is the product of the convolution arguments.

Now that's a sweet math trick.

$
I don't know if that's a trick so much as the purpose of the Laplace Transform.
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Old 04-25-07, 08:13 AM
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Did you know that 142.857 is a curious number?

142.857 x 2 = 285.714 ( same digits )
142.857 x 3 = 428.571 idem
142.857 x 4 = 571.428 idem
142.857 x 5 = 714.285 idem
142.857 x 6 = 857.142 idem
142.857 x 7 = 999.999 !!!
142.857 x 8 = 1.142.856 (number missing is 7, but last -6- and first -1- add to 7
142.857 x 9 = 1.285.713 (number missing is 4, but last and first add to 4 )

You can go on and on...



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Old 04-25-07, 09:21 AM
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Quote:
Originally Posted by Matias View Post
Did you know that 142.857 is a curious number?

142.857 x 2 = 285.714 ( same digits )
142.857 x 3 = 428.571 idem
142.857 x 4 = 571.428 idem
142.857 x 5 = 714.285 idem
142.857 x 6 = 857.142 idem
142.857 x 7 = 999.999 !!!
142.857 x 8 = 1.142.856 (number missing is 7, but last -6- and first -1- add to 7
142.857 x 9 = 1.285.713 (number missing is 4, but last and first add to 4 )

You can go on and on...




This one is the key to all that. Multiples of 9 produce a lot of odd number things.

Remember the way the whole 9 times table added up to 9?

9 x 1 = 09 ; 9 + 0 = 9
9 x 2 = 18 ; 1 + 8 = 9
9 x 3 = 27 ; 2 + 7 = 9
9 x 4 = 36 ; 3 + 6 = 9
9 x 5 = 45 ; 4 + 5 = 9
9 x 6 = 54 ; 5 + 4 = 9
9 x 7 = 63 ; 6 + 3 = 9
9 x 8 = 72 ; 7 + 2 = 9
9 x 9 = 81 ; 8 + 1 = 9
9 x 10 = 90 ; 9 + 0 = 9

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Old 04-25-07, 10:25 AM
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