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 AUTHOR
 Revilors
Joined: 10/9/2008
Msg: 1
Mathematical Black Hole?Page 1 of 2    (1, 2)
Three guys decide to order pizza delivery. They each have a ten dollar bill in their wallet. They order pizza…and the pizza guy shows up with the food and tells them it will be $30 even. “Great”, they said “but sorry, we haven’t enough for a tip”.

The pizza guy gets back to the store and hands the money to the manager. The manager rings up the order and discovers that the order was eligible for a five dollar discount. He takes five one dollar bills from the till and instructs the delivery driver to return the money.

On the way…the driver decides that since he has no change and there are three guys…he’s going to give each guy one dollar and keep two for himself as he has now made two trips without a tip.

He gives each guy a dollar (they have now effectively paid nine each) and keeps two for himself.
9 x 3 = 27 + 2 = 29.

WTF happened to the other dollar?

I can work this from a couple of different angles and make sense of it. But when I follow the money this way…one dollar disappears. Is this a mathematical black hole?

Edit:

I actually took five minutes and figured it out now.

Funny how the brain can easily trick itself.

Did it get you...temporarily?
 Jazzzy
Joined: 10/17/2006
Msg: 2
Mathematical Black Hole?
Posted: 9/3/2011 4:57:19 PM
Pizza math? dude.. you need a hobby.
 Revilors
Joined: 10/9/2008
Msg: 3
Mathematical Black Hole?
Posted: 9/3/2011 5:01:46 PM
Pizza math? dude.. you need a hobby.


It was a puzzle my daughter gave me.

She is my hobby
 Jazzzy
Joined: 10/17/2006
Msg: 4
Mathematical Black Hole?
Posted: 9/3/2011 5:04:29 PM
I love puzzles.. Jenga rules
 HalftimeDad
Joined: 5/29/2005
Msg: 5
Mathematical Black Hole?
Posted: 9/3/2011 5:32:42 PM
That one stumped me when I was a kid. It's pretty simple now though.
 nipoleon
Joined: 12/27/2005
Msg: 6
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History
Mathematical Black Hole?
Posted: 9/4/2011 1:39:26 AM
You've never read the annual shareholders report from a publicly traded company before, have you ?
 Revilors
Joined: 10/9/2008
Msg: 7
Mathematical Black Hole?
Posted: 9/4/2011 6:19:46 AM

You've never read the annual shareholders report from a publicly traded company before, have you ?


In the words of perhaps one of the brightest minds in history.....Larry the Cable Guy...."I don't care who you are...that's funny".
 Lint Spotter
Joined: 8/27/2009
Msg: 8
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Mathematical Black Hole?
Posted: 9/4/2011 8:33:55 AM
Brilliant... I love brain teasers. Excellent one OP...

Pizza math? dude.. you need a hobby.
I work with a guy that has programmed a pizza calculator... I use to scoff at it, until I realized that I've spent more time figuring out in my head how many pizzas to order than he spent building the calculator. I've since asked him to convert it to burgers and hotdogs...
 2findU
Joined: 11/19/2005
Msg: 9
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Mathematical Black Hole?
Posted: 9/4/2011 6:36:12 PM
It sure isn't 9 x 3, sure that equals 27 but its 30-5 = 25, 25/3 = 8.3333333.

So the delivery driver returns $1.00 to each of them. So that makes 9.33333 ea.
9.333333 x 3 = 28.00, so 28 + 2 (the tip) = 30.

Just 8th grade algebra, no mathematical black hole. You're equation was do to incorrect logic.
 RandomScause
Joined: 8/16/2011
Msg: 10
Mathematical Black Hole?
Posted: 9/4/2011 6:47:48 PM
Another brain teaser:

A young mathematician looks at the old mathematician who is giving a lecture in a universety class, and the young mathematician thinks along these lines:

"I am your son, but you are not my father."

How is that possible?

Hint: No relgious considerations.
 Revilors
Joined: 10/9/2008
Msg: 11
Mathematical Black Hole?
Posted: 9/4/2011 7:33:23 PM

It sure isn't 9 x 3, sure that equals 27 but its 30-5 = 25, 25/3 = 8.3333333.

So the delivery driver returns $1.00 to each of them. So that makes 9.33333 ea.
9.333333 x 3 = 28.00, so 28 + 2 (the tip) = 30.

Just 8th grade algebra, no mathematical black hole. You're equation was do to incorrect logic.


Not 8th grade algebra...but rather 3rd grade math.

You are wrong.

They did each pay 9 dollars. 9 x 3 =27. 25 for the pizza and 2 for the tip.
With three dollars left in their wallets...makes the 30 dollars accountable.

Keep the change.


Edit for above.

The older one is his mother
 cbbull21
Joined: 3/9/2009
Msg: 12
Mathematical Black Hole?
Posted: 9/4/2011 7:36:32 PM
Helga not Herald is the Professor
 chrono1985
Joined: 11/20/2004
Msg: 13
Mathematical Black Hole?
Posted: 9/4/2011 9:45:15 PM
Didn't really get me at all. But then I'm the type of person to look at solution to a problem, see the flow, and write my own solution.

The real mathematical black hole is if they paid with credit card !
 RandomScause
Joined: 8/16/2011
Msg: 14
Mathematical Black Hole?
Posted: 9/5/2011 12:03:13 PM
I think you are right, CBBull21.

I never got the solution to this problem either, at least not by figuring it out.
 Revilors
Joined: 10/9/2008
Msg: 15
Mathematical Black Hole?
Posted: 9/5/2011 1:46:30 PM
Sorry...double post
 Revilors
Joined: 10/9/2008
Msg: 16
Mathematical Black Hole?
Posted: 9/5/2011 1:48:11 PM
30-3=27. They paid 27 bucks. 25 for the pizza and 2 for the tip.

27 /3=9 They paid 9 dollars each. Which is evident by the fact that they each had 10 to begin with...and now each have one.

I kinda felt foolish that this one "got" me for like 5 minutes. Feelin' better now.

The trick is that you get stuck on the original number of 30.


wow.....they really each paid 9. $27 total, 25 to the restaurant and 2 to the driver. The error is to think they paid 10.

Why do people have so much trouble with that?


+1. Or...does that equal 31 now
 RandomScause
Joined: 8/16/2011
Msg: 17
Mathematical Black Hole?
Posted: 9/6/2011 1:11:46 PM
So, they paid $25 for the pizza actually.
And they got $3 back which = $28


Why in the world are you adding an amount they paid to an amount they got back???

The only part of this I don't understand is how this confuses some people.

----------------

This, by Alan.

Alan, it confused me for like 27 years. I heard this puzzle first stated to me when I was 30, I think.

"They do it with smoke and mirrors."

-------------

I got paid $1000 for doing some work. I spent $500 on some computer gear, which = $1500....I mean it makes no sense.

- - - - - - - -

What I do know is that I repaired three computers in my entire life, and I am now a multi-millionnaire, and a self-made-man at that.
 RandomScause
Joined: 8/16/2011
Msg: 18
Mathematical Black Hole?
Posted: 9/6/2011 1:18:32 PM
An old farmer is dying.

He calls his three sons to his deathbedside.

"Alan... you are the oldest and the smartest. You get 1/2lf of my horses.

Piglet... you are the second oldest and the second smartest. You get 1/3rd of my horses.

Goober... you are the youngest and third smartest... and I think your real father is the John Deere salesman, really... you get one/9th of my horses."

The old man dies. He left seventeen horses behind which he could not take with him.

The boys did not want to divvie up the horses by hatchet.

What could they do? (trickiness level: Grade 231.)

---------------

Edit: I first heard it at age 5, and my brother's best friend's father's dentist, who was eating with us in the concentration camp, told us the answer seven years later. Mom always knew the answer, but she kept mum about it. She wanted us kids to be so smart as she. By working our minds. For the FYI-minded ones of you, she failed.

(*) Not a Nazi concentration camp, but a communist forced labour camp in Hungary. But hey, who could tell the difference?
 Revilors
Joined: 10/9/2008
Msg: 19
Mathematical Black Hole?
Posted: 9/6/2011 5:44:19 PM
I'm going to guess he had 18 horses...was buried with one and left 17 "behind". He "took one with him".

Half of 18 is 9 for the Eldest.
Third of 18 is 6 for the next.
1/9 of 18 is 2 for the last.

9 + 6 + 2 = 17
 RandomScause
Joined: 8/16/2011
Msg: 20
Mathematical Black Hole?
Posted: 9/6/2011 10:10:46 PM
Alan: You got the answer I heard in my childhood.

Relivors: You got a more sophisticated answer. Not mathematically, but anthropo-religio-mythology-wise.

I have a third puzzle, which I solved on my own. It was in a grade seven textbook in Hungary, about twenty years after I left the country. This puzzle is easy to mix up in the setting-up of it, so please bear with me.

------------

Hey, John! Haven't seen you since high school. You live here?

Yes, right in this house behind me. Good to see you!!

John, you got married? Kids? How many? Age?

Well, yes I got married, and have three kids. They are... hey, you still goobery about math?

Yes, John.

Okay. I have three kids. If you add their ages, you get today's date.

That's not inidicative in any big way, John.

Right. But if you multiply their ages, you get my house number.

Right... right... still indeterminant.

Well. The oldest one had his birthday last week.

Ha!! I know their ages now.

----------
I heard really smart people say this story really stupidly. They mauled the story, gave hints that are extrenous, and still managed to say the riddle so that it would remain unsolvable.

The question is, of course, what are the ages of the three kids.

Hint 1: I did not mess up any part of the story.
Hint 2: you need no hints other than the reassurance I've given, to determine the kids' ages exactament.
 RotationAxle
Joined: 7/20/2011
Msg: 21
Mathematical Black Hole?
Posted: 9/9/2011 1:04:14 AM
Yeah, I was stuck on this for a few minutes myself! I've never seen this one before.

I subtracted 5 from 30 and added 3 to get 28...then add two more to get 30 again.

Good post!
 2findU
Joined: 11/19/2005
Msg: 22
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Mathematical Black Hole?
Posted: 9/10/2011 11:18:10 AM

I'm going to guess he had 18 horses...was buried with one and left 17 "behind". He "took one with him".

Half of 18 is 9 for the Eldest.
Third of 18 is 6 for the next.
1/9 of 18 is 2 for the last.

9 + 6 + 2 = 17


I came up with the same solution. I didn't scroll down until I worked it out.
 Revilors
Joined: 10/9/2008
Msg: 23
Mathematical Black Hole?
Posted: 9/12/2011 3:40:28 PM

You're right when you multiply 3 by 9: The three customers paid a total of $27. but why are you adding two to it? And why are you wanting it to add up to $30? What meaningful quantity do you expect to get when you add the net money paid by the customers to the money kept by the driver??

Yes, the customers, net, paid $27. Two of it is in the wallet of the driver. The other $25 of it is in the cash register of the pizzaria. What's the problem?

And, of the original $30, $25 of it is in the cash register, two is in the driver's wallet, and three have been returned to the customers. No problem there either.


Yeah...thanks Johnny Come Way Lately. I guess you didn't read the whole thread. We covered that.
 Revilors
Joined: 10/9/2008
Msg: 24
Mathematical Black Hole?
Posted: 9/12/2011 3:56:50 PM

Is that what you call it? :-) What did you cover it with? :-)

Yes, one or two people said it right. But some of you continued to be lost in confusion.

I don't care if someone else said it right. Some of you kept getting it wrong.

The question was asked. I answered it. I don't deny credit to anyone else who answered it too.


No...it was answered by several other and your re-posted their answer.

Including mine

Posted by me...


Post #11

Not 8th grade algebra...but rather 3rd grade math.

You are wrong.

They did each pay 9 dollars. 9 x 3 =27. 25 for the pizza and 2 for the tip.
With three dollars left in their wallets...makes the 30 dollars accountable.

Keep the change.


and



Post #20
30-3=27. They paid 27 bucks. 25 for the pizza and 2 for the tip.

27 /3=9 They paid 9 dollars each. Which is evident by the fact that they each had 10 to begin with...and now each have one.


Yet you chose to quote me...and then copy my answer. Whatever
 Revilors
Joined: 10/9/2008
Msg: 25
Mathematical Black Hole?
Posted: 9/12/2011 4:55:50 PM
It's all just a silly example of how the mind can play tricks on itself. Even if it's only temporarily.

Years ago...we were in Yellowstone driving on a narrow highway. When off in the distance...one of the kids saw a bear fishing in the stream. Then...we all saw it and pulled over to take a closer look at the sight of this animal in nature. It wasn't long before there were 15 or 20 cars backed up on the highway. And...30 or 40 people behind and beside us witnessing the awe inspiring sight. Then...almost at the same time...we secretly suggested that it looked a lot like a rock in the stream. And sure enough...it was.

We slowly and deliberately backstepped our way through the crowd until we could make our escape. Still oooohing and aaahhhing we left them and the people yet to join them. We laughed about the people still there...but more at ourselves for unwittingly starting the whole charade.

It's all good clean fun.
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