The Naked Scientists

The Naked Scientists Forum

Author Topic: 30=29  (Read 4542 times)

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
30=29
« on: 12/11/2005 14:16:37 »
I know this is an old chestnut that has been regurgitated in classrooms & bars across the world ad nauseam, possibly causing punch-ups & maybe even the odd revolution in banana republics, but here it is once more just on the offchance someone has been living in a cave all their life.

3 men go to buy a television. They find 1 for 30 and pay 10 each (they must have gone to Cash Converters! :D). When they've left the shop, the assistant realises the television was on offer & he should have only charged them 25. He runs after them (obviously NOT Cash Converters!) but instead of giving them back the 5 he gives them each 1 & pockets the other 2 himself.
So, having initially paid 10 each, when the 3 men get 1 each back, they have paid 9 each & the shop assistant has 2.
3x9=27+2=29. Where is the other 1?

I remember sitting in maths (yes, Americans... it's MATHS - PLURAL!)class at school, scribing away on my slate tablet, & puzzling over this. When I asked my teacher to explain it he soundly thrashed me (for which I am, of course, eternally grateful) & told me not to be insolent.
Since then I have asked numerous people & not yet had a satisfactory answer. Can any of the whizzo maths bods here explain it for me? I would hate to meet my maker not knowing the answer.

Thank you [:o)]

(I've just had a vision of George Dubya - "Hell, I don't know the answer. Didn't the Ay-rabs invent arithmetickle? Well, let's invade Eye-rack")
« Last Edit: 12/11/2005 14:22:03 by DoctorBeaver »


 

Offline ukmicky

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 3011
    • View Profile
    • http://www.space-talk.com/
Re: 30=29
« Reply #1 on: 12/11/2005 15:04:57 »
arrrrrrrrrrrrrrrrrhhhhhhhhhhhhhhhhhhhhhh bastard:D:D

Michael                                      
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: 30=29
« Reply #2 on: 12/11/2005 15:15:10 »
I know, I know !!! While each of the men has indeed paid a net 9  this is balanced by the 2 in the assistants pocket and the 25 back at the store.

The final calculation, adding the 27 and the 2 is where the "paradox" arises - the 2 should be subtracted, since the total spent was 27, 25 for the TV and 2 for the delivery of the refund..........errr...does that make sense ?

Men are the same as women.... just inside out !!
 

Offline ukmicky

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 3011
    • View Profile
    • http://www.space-talk.com/
Re: 30=29
« Reply #3 on: 12/11/2005 15:26:20 »
No:)

Michael                                      
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: 30=29
« Reply #4 on: 12/11/2005 20:09:25 »
Excellent, glad I could help !!...  :-)

Men are the same as women.... just inside out !!
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: 30=29
« Reply #5 on: 22/11/2005 03:26:33 »
Neil - that's all very well but it doesn't explain the paradox. The bottom line is that they have paid 9 each & the shop assistant has 2. If you subtract the 2 from the 27 you've only got 25 which means that 5 is missing!

quote:
the 2 should be subtracted, since the total spent was 27, 25 for the TV and 2 for the delivery of the refund


That means 3 is missing

[xx(]
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: 30=29
« Reply #6 on: 22/11/2005 03:53:44 »
Look at it this way Eth.

In the shop till is 30, the assistant takes 5 to refund. Leaving 25 in the till...ok ?...He gives 3 back and pockets 2...

2 in pocket plus 3 refund plus 25 in shop till = 30....The 27 that they have paid is comprised of the 25 in the till and the 2 in the pocket of the assistant.......YAYYYYY !!

Men are the same as women.... just inside out !!
« Last Edit: 22/11/2005 03:57:05 by neilep »
 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: 30=29
« Reply #7 on: 22/11/2005 12:52:41 »
Very clearly explained, Neil - top marks again!

Doc - in case you still don't get it, try thinking of it this way: the 30 is really a bit of a red herring.  Imagine if the story went like this:

"3 men go to buy a television. They find 1 for 27 and pay 9 each.  When they've left the shop, the assistant realises the television was on offer & he should have only charged them 25. He pockets the other 2 himself."

Now it's clear that the calculation "3x9=27+2=29" is meaningless. Whereas the calculation "3x9=27-2=25" does mean something - it's the amount of money in the till.

QED


"Do infants enjoy infancy as much as adults enjoy adultery?"
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: 30=29
« Reply #8 on: 22/11/2005 13:13:38 »
But what about V.A.T.?
 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: 30=29
« Reply #9 on: 22/11/2005 15:32:25 »
I understand your problem now. It's not a mathematician you need, it's a tax accountant.:D

(And they really CAN work magic with numbers.)

"Do infants enjoy infancy as much as adults enjoy adultery?"
 

The Naked Scientists Forum

Re: 30=29
« Reply #9 on: 22/11/2005 15:32:25 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums