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1

Uhhhhhhhhhhhhhhhhhhhhhhh

Work backwards?

No fuckin clue.

Posted by Jeff | April 20, 2007 11:44 AM
2

Trippy

Posted by elswinger | April 20, 2007 11:45 AM
3

Maybe I did it wrong...what's the answer supposed to be?

Posted by Kate | April 20, 2007 11:46 AM
4

x=first three digits
y= last four digits

250(80x+1)->
20,000x +250->
20,000x +250 +y ->
20,000x +250 +2y ->
20,000x + 250 +2y -250 ->
10,000x +y ->

basically a lot of math to multiply the first three digits by 10,000 and then add the last four digits

Posted by arduous | April 20, 2007 11:48 AM
5

So, as a forumla this is:


(((80x + 1) * 250 + 2y) - 250) * 0.5


where x is the first three digits of your phone number and y is the last four digits.


We can reduce this as follows:

0.5 * ((80x + 1) * 250 + 2y) - 125

(80x + 1) * 125 + y - 125

125 * 80x + 125 + y - 125

125 * 80x + y

10000x + y


Note that the effect of multiplying by 10000 is to shift the first three digits of your phone number left by four digits, effectively "making room" for the last four digits.


So really someone just did the simple thing (multiply by 10000) then factored in a bunch of silly ways to obfuscate what they were doing. That's pretty much the standard operating procedure for stuff like this.

Posted by Habib | April 20, 2007 11:48 AM
6

1. Key in the first three digits of your phone number (NOT the area code)

2. Multiply by 10,000.

3. Add the last 4 digits of your phone number...

look familiar?

amazing!!! how can math possible do such amazing things???

Posted by infrequent | April 20, 2007 11:49 AM
7

A=prefix B=4 digit number

Formula [(80A + 1) x 250 +B +B -250]/2

= [20000A +250 +2B -250]/2

=[20000A +2B]/2

= 10000A +B

Plug in A say 323 and it becomes 3230000 and B 7101 add them together and you get

3237101

Posted by Kush | April 20, 2007 11:49 AM
8

Damn, you beat me to it. And it's not THAT arduous.

Posted by Noink | April 20, 2007 11:49 AM
9

Well, they ask you for your phone number so they pretty much just make you jump through hoops before they give you back what you put in.

It's like a psychic telling you exactly what you've told them and making it sound like they already knew.

Posted by Carollani | April 20, 2007 11:50 AM
10

oh, those are arrows at the end. i realized too late that that looked weird.

Posted by arduous | April 20, 2007 11:50 AM
11

[condescension]

1. Key in the first three digits of your phone number (NOT the area code)

2. Multiply by 10,000.

3. Add the last 4 digits of your phone number...

look familiar?

amazing!!! how can math possible do such amazing things???

[/condescension]

Posted by infrequent | April 20, 2007 11:50 AM
12

Well, there seem to be a lot of steps added in just to make things seem more complicated than they are. You're actually just adding the last 4 digits of your telephone number (let's call them "defg") to the first 3 (called "abc") times 10000.

In other words: (abc x 10000) + defg = abcdefg.

I've broken it down into three parts where the puzzle maker tried to confound what's actually happening. Here they are:

1)80x250=20000
20000/2 = 10000
10000x(abc)= abc0000

2)80+1=81
81x250=20250
20250-250 = 20000
20000/2 = 10000
10000x(abc) = abc0000

3)(defg)+(defg) = 2d2e2f2g
2d2e2f2g = 2(defg)
2(defg)/2 = defg
abc0000+defg = abcdefg

I know that's not a very mathematically correct way to show how this works, but it makes sense to me.

Posted by oigo | April 20, 2007 11:55 AM
13

As a case of obfuscation, though, it's pretty damned brilliant. At no point does a suspicious "1,000" or other large round number even enter the picture, and half of the operations seem designed to undo the damage you did by simply adding 1. Very nicely done!

Posted by Wordboy Dave | April 20, 2007 11:57 AM
14

Well done, fellow math nerds!

You will also note that the rule about not using the area code is pure stagecraft. But isn't that the whole point?

Posted by Bryan in the UK | April 20, 2007 12:00 PM
15

Oops, I guess what I said in post 14 isn't quite true; the effect wouldn't be as cool if you gave it your area code and the last four digits, then it just spat them right back out in order.

Won't some enterprising soul come up with a version that also incorporates the area code? Then it will look even more convoluted and impressive!

Posted by Bryan in the UK | April 20, 2007 12:06 PM
16

Wow, all these math nerds at the slog is kinda sexy!

Posted by catnextdoor | April 20, 2007 12:08 PM
17

Congratulations, Dude.

You've just given over your phone number to The Man.

Posted by NapoleonXIV | April 20, 2007 12:17 PM
18

i know!!! i'm crank calling
ABC-DEFG right now!!!

Posted by infrequent | April 20, 2007 12:33 PM
19

Math is hard

Posted by monkey | April 20, 2007 12:36 PM
20

To paraphrase the late Mr. Vonnegut, if you think Arabs are stupid, remember that they gave us our numbers -- try doing that trick with Roman numerals.

Posted by --MC | April 20, 2007 12:47 PM
21

arabs are stupid. after all, they're monotheists.

Posted by maxsolomon | April 20, 2007 12:54 PM
22

Wow, y'all's a bunch of math-e-ma-JISH-uns. PS-I wish I still had the frame of mind to figure that out. And I'm only 23. I've peaked.

Posted by Ryno | April 20, 2007 12:58 PM
23

Just for Dan - no help from the audience

Three businessmen need a hotel room (this is an old riddle) and the clerk gave them a room for $30 - after they went up he realized that he had overcharged for the room, it was really only twenty-five dollars. He called the bellhop over and sent him up with 5 one dollar bills to give the men a refund. The bellhop couldn't figure out how to divide the five among three so he gave them each one dollar and kept two for himself. So each of the men paid $9 dollars or a total of $27 and the bellhop has $2 for a total of $29 - what happened to the missing dollar?

Now give Dan some time.

Posted by Kush | April 20, 2007 1:20 PM
24

@23: some kind of magic tax? This is what happens when Democrats control Congres....

Posted by el ganador | April 20, 2007 1:24 PM
25

@20:

Grab a calculator.

1. Key in the first three digits of your phone number (NOT the area code)

2. Multiply by LXXX

3. Add I

4. Multiply by CCL

5. Add the last IV digits of your phone number

6. Add the last IV digits of your phone number again

7. Subtract CCL

8. Divide by II

Recognize the answer?

Posted by so it goes | April 20, 2007 1:24 PM
26

@15: My math’s rusty, but this version including the area code should work…

1. Key in your area code

2. Add your area code again

3. Multiply by 500

4. Add the first three digits of your phone number (NOT the area code)

5. Multiply by 80

6. Add 1

7. Multiply by 250

8. Add the last 4 digits of your phone number

9. Add the last 4 digits of your phone number again

10. Subtract 250

11. Divide by 2

Posted by JME | April 20, 2007 1:33 PM
27

where exactly is this $25 room? i'd le the bellhop keep the $2 for that price. i mean, have you seen rental rates lately?

Posted by infrequent | April 20, 2007 1:35 PM
28

I'm just impressed that really smart people have as much time to waste as I do reading this blog and all the comments.

Posted by Bill LaBorde | April 20, 2007 4:53 PM
29

I know the missing dollar answer. Is Dan stoned yet?

Posted by glasspusher | April 20, 2007 10:15 PM
30

All math tricks are purdy much the same. Not impressive.

Posted by Lisa | April 21, 2007 5:09 AM
31

I give up. Someone explain the hotel thing to me. I always use Priceline, so I never get refunds -- is that why I can't work this out?

Posted by Dan Savage | April 21, 2007 9:39 AM
32

The hotel riddle basically screws your head by purposely mixing up information. There's no missing dollar. The bellhop's $2 comes out of the $27 total that was paid.

From the businessmen's perspective, they paid the hotel $10 each and each received a $1 back. So the hotel got $27 and they have the remaining $3. (3x9)+(3x1)=27+3=30

From the bellboy's perspective, the hotel got $25, he skimmed $2 and the remaining $3 went to the business men. 25+2+3=30

Posted by Aexia | April 21, 2007 1:03 PM
33

I dont get it?

Posted by Ashley | April 27, 2007 4:52 PM

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