Math Problem

[Barbeque Senior Member Find all posts View Profile Close Barbeque]

UNBELIEVABLE MATH PROBLEM


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.
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...got that Dave!!! ;-) )
2. Multiply by 80
3. Add 1
4. Multiply by 250
5. Add to this the last 4 digits of your phone number
6. Add to this the last 4 digits of your phone number again.
7. Subtract 250
8. Divide number by 2

Do you recognize the answer ??

[bigfrank Administrator Find all posts View Profile Close bigfrank]

Do you recognize the answer ??

No, but the first 3 #'s are my cell and the last 4 are my cell cut in half.

[Lanalee Senior Member Find all posts View Profile Close Lanalee]

It worked for me. The final answer is my complete home phone number. I tried it with my cell phone number, and it worked with that number too!

Very impressive. Someone has lots of time of their hands!

[Faust Super Moderator Find all posts View Profile Close Faust]

It works,
That’s my number

[IreneLF Senior Member Find all posts View Profile Close IreneLF]

it was my full phone # - how ? I want someone to explain this please

[T. R. Oglodyte Moderator Find all posts View Profile Close T. R. Oglodyte]

It's simple algebra. I'll take you through.

To start, let's represent your phone number as abc-defg where the letters are the respective digits in your phone.

To avoid cluttering up things with zeros, I'm going to use scientific notation and use a "^" symbol to represent the exponent (just as you do in an Excel spreadsheet).

Accordingly:

10^2 = 100
10^3 = 1000
10^4 = 10,000
10^5 = 100,000
10^6 = 1,000,000

Also, "*" is the symbol for multiplication. So 3*10^3 = 3*1000 = 3000.

Now let's work our way through the steps in the problem.

1. Here you are entering the first three digits of your phone as if it were a three digit number. Note that the number abc can be expanded to:
   
   10^2*a + 10*b + c
2. Now you multiply that number by 80, so now you have:
   
   80*10^2*a + 80*10*b + 80*c.
   
   That reduces to:
   
   8*10^3*a + 8*10^2*b + 80*c.
3. Now add 1 to that number:
   
   8*10^3*a + 8*10^2*b + 80*c + 1
4. Multiply by 250
   
   I'll go straight to the simplified result:
   
   2*10^6*a + 2*10^5*b + 2*10^4*c + 250
   
   At this point I'm going to partially collapse this number (the opposite of the expansion in step 1) so you can see where we are:
   
   2*(abc0000) + 250
   
   Notice how everything we've done so far puts the first three digits of your phone in order as the first three digits of a seven digit number. At this point all we have to do is get the last four digits added to that number and clear out the clutter and we will be back to your original phone number. That's what the remaining steps do.
   
   
5. We now add the last four digits of your phone number
   
   2*(abc0000) + defg + 250
6. We now add the last four digits of your phone number again
   
   2*(abc0000) + 2*defg + 250
   
   You ought to be able to see where this is going. I further simplify this to:
   
   2*(abc0000 + defg) + 250
   
   If I add together abc0000 + defg, I get:
   
   2*abcdefg + 250
   
   abcdefg, of course, is your original phone number. So at this point the number in your calculator is twice your original phone number, plus 250.
   
   
7. Now we subtract away that 250, leaving:
   
   2*abcdefg
8. Dividing that by 2 leaves you with abcdefg, your original phone number.

[IreneLF Senior Member Find all posts View Profile Close IreneLF]

"At this point all we have to do is get the last four digits added to that number and clear out the clutter and we will be back to your original phone number. That's what the remaining steps do."

Thanks Steve. This was helpful. I couldn't see how express it, to clear out the junk and make it work.
My two kids taking algebra might like this one. I'm curious to see if DD's math teacher can explain it. (bet not and best not to put him on the spot!)

[chellej Senior Member Find all posts View Profile Close chellej]

[QUOTE=Barbeque;121718]UNBELIEVABLE MATH PROBLEM


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.
....


So does that mean we're starting a write in campaign for Steve Nelson for President?????

[The Conch Man Past Goumba President & BigFrank's Cigar Buddy! Find all posts View Profile Close The Conch Man]

Back in my younger days Steve ~~ I'd remember what ya say in your reply ~~ Way-to-comlicated for me these days ~~ but ya do have it right ~~ Congrats on a well done job ~~