Riddle

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Posted: Thu Jul 19, 2007 12:05 pm

anyone care to solve the following riddle?

Three chaps decide to order a $10 pizza each.
Half an hour later the delivery man arrives with three pizza's and they pay him $10 each.
When the delivery man returns to the Pizza place and deposits $30 in the till, the manager says "Hang on, there's a special offer going on : 3 pizza's for $25, go and give them $5 back".
On his way to return the money, the delivery man thinks "hey, they can't split $5 three ways, and they didn't even give me a tip, so I'll take $2 for myself, and return $3".
He arrives and explains there was a special promo : 3 pizza's for $27, and he gives them $1 each.
This means each of the men has actually paid $9 (10-1).
$9 x 3 = $27
The delivery man has put $2 in his pocket.
$27 + $2 = $29
So where's the remaining dollar? :shock:

Never mind the inconsistencies of the story (yea right, the manager would really return the $5... or even more ludicrous : the delivery chap wouldn't pocket the whole $5)...

Feel free to use in baits (the Mugu who finds the answer will be rewarded $10.000... or something of the sort...)

Posted: Thu Jul 19, 2007 12:16 pm

Each guy did pay $9. Then, $2 of the $27 went to the delivery boy (!), and the other $25 went to the pizza place. The trick is where you add the $2 to the $27 collected. That shouldn't be there. I'm sure Doctor X will come along shortly to write a multi-page abstract explaining the mathematical grounds for this common misunderstanding in more detail. Wink

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

I know.

As in all these riddles, the question reverses the maths in a way that sounds right but is not. In this case the customers are told pizza comes to $27, so the delivery man returns $3. 3+27=30, but in fact it came to $25. The delivery man kept $2: 25+2=27, and returned $3: 27+3=30. The $3 between 27 and 30 is the three dollars returned to the customers, not the two dollars retained by the delivery man.

I'll donate the 10,000 to eater.
Damn. Beaten by Don

Posted: Thu Jul 19, 2007 12:20 pm

Yep 25 in the till, 3 to the customers and 2 to the delivery boy, You confuse the person your telling it to by adding the 27 and the 2 together

Heres one: (Probably really old, derived from a chain email I think.)

"Think of words ending in -GRY. Angry and hungry are two. There are only three words in the English language. What is the third word? The word is something that everyone uses every day. If you have listened carefully, I have already told you what it is."

Posted: Thu Jul 19, 2007 12:32 pm

language ??

Posted: Thu Jul 19, 2007 12:34 pm

Posted: Thu Jul 19, 2007 2:46 pm

Ooo!! Ooo!! Me!! Me!! jump_4_joy

The money got dropped on the ground and stuck to the gum on the underside of someone's shoe! Very Happy

Posted: Thu Jul 19, 2007 3:00 pm

Reaper-

That is the worst riddle ever. That would have made sense had the sentence been written with quotation marks aroung "the English language". This riddle really only works when spoken. Even then, it sucks.

Posted: Thu Jul 19, 2007 3:37 pm

Here's one that had me stumped for a while:

You're on a game show. There are twenty doors. Behind one, there is a trunk box full of money. Behind the other nineteen there are goats. You pick one door. The host, with much drama and suspense, opens 18 doors to reveal goats.

There are now two doors left, one has a goat, and one has the money. Before opening the next door, the game show host offers you a chance to switch doors.

Here's the question: will your odds of walking away with the trunk box be improved if you switch?

Posted: Thu Jul 19, 2007 4:20 pm

(my) logic would tell me no, but then choosing the illogical explanation I'll say yes ! Laughing

Actually, there a gameshow televised over here where 20 contestants are given a box each. Each box containes a certain amount of money, ranging from 50 Eurocents to 100.000 Euro. One contestant is then "chosen at random" and can choose the other contestant's boxes, one at a time. Once chosen, the other contestant then has to open his box and reveal the amount that was in it. This amount then is deleted from the board... The chosen contestant can at regular times choose the amount the "bank" offers (usually an amount which is the average of the remaining amounts...), but he then can not continue the game.
Most people are greedy and continue.
I've seen this game in 3 different countries and the rules vary slightly, but over where I live, if there are only two boxes left (the chosen contestant's and the remaining contestant's box), the bank often, instead of offering an average amount, offers the contestant the option of switching boxes... Most contestants do not switch and are subsequently more often than not ....fXXXed

Posted: Thu Jul 19, 2007 4:33 pm

You are correct, and the contestants you mentioned who do not switch are dramatically reducing their odds of winning by not switching.

It seems like the odds should be 50/50. After all, regardless of what happened previously, in the end there are only two doors; one with a goat, and one with a box of money. Right?

So why are the odds not 50/50?

Posted: Thu Jul 19, 2007 4:41 pm

It is mathematical. His original pick has a 1 in 20 chance of being correct, even though you have eliminated 18 already, it is still 1 in 20 or 5%. The new choice is 1 in 2 or 50%. Just because you know that 18 have goats now, you didn't know that when you picked.

Posted: Thu Jul 19, 2007 4:47 pm

^^^ yes, but he has the equal 50/50 chance whether he switches or not. At this point there are two choices and the last 18 are no longer relevant. He can't improve his chance by switching. (Edit: Ook, now I see what you mean. You're right, of course.)

Wait a min. His chances of 1/20 of getting it right the first time haven't changed either. So it's 1/20 if he sticks and 1/2 if he switches? Or is it 19/20 to switch...I'm so confused...

Embarassed

Posted: Thu Jul 19, 2007 4:49 pm

the dollar was sent to Usm2n B3llo via western union

Posted: Thu Jul 19, 2007 4:54 pm

ratter wrote:

Wait a min. His chances of 1/20 of getting it right the first time haven't changed either. So it's 1/20 if he sticks and 1/2 if he switches

This is correct.

Posted: Thu Jul 19, 2007 5:01 pm

^^Well done. As a reward, I'll give you the trunk box. Unfortunately, the money in it has been printed over with black ink. What are the odds that my patented cleaning solution will work?

Edit: my spelling is worse than my math.

Posted: Thu Jul 19, 2007 5:03 pm

^^^^^ 1/infinity, more or less....

@Ook, you say I'm right that it's 1/20 to stay, 50/50 to switch...don't the chances have to add to one if they are mutually exclusive? 1/20 and 19/20?

Posted: Thu Jul 19, 2007 5:19 pm

^^ I think that is correct.

Here's an explanation: http://www.faisal.com/docs/monty.xhtml

Posted: Thu Jul 19, 2007 5:21 pm

Same as the pizza money, adding apples and pears.
chance 1/20 to pick the right one out of 20 or 19/20 to pick the wrong one

chance 1/2 to pick the right one out of 2 or 1/2 to pick the wrong one

Posted: Thu Jul 19, 2007 6:13 pm

back to the pizza money - The EXACT answer is that the other dollar is in the cash register at the pizza place!!!

Because - - how do you divide 25 by 3? You do not....24 is the closest #. So the guys were to really pay about $8.33 each. So he then gave them each $1. This then means he pockets $2.......and when you did the math the other way......the extra dollar was......in the cash register at the pizza store!

Posted: Thu Jul 19, 2007 6:13 pm

Eater is repeating itself:

http://forum.419eater.com/forum/viewtopic.php?p=793382#793382

Posted: Thu Jul 19, 2007 6:25 pm

@Ratter - sorry you are right, it is switching from 1/20 to 19/20 the percentage still has to equal 100. I forgot that little rule. So it is almost always to your advantage to switch.

Posted: Thu Jul 19, 2007 7:17 pm

x = .9 (repeating)
10x = 9.9(repeating)
10x = 9 + x

subtract x from both sides

9x = 9

x = 1

.9(repeating) = 1

Shocked

Posted: Thu Jul 19, 2007 7:46 pm

^^^^^
By just saying repeating you are losing the thought of infinity. The problem is unsolvable because you have introduced infinity. There is no true end to the number .9(repeating), so in a way it is 1.

Let's examine 1/3's.
1/3 = .3(repeating)
2/3 = .6(repeating)
Since
1/3 + 2/3 = 3/3 or 1
and
.3(repeating) + .6(repeating) = .9(repeating)
Then
.9(repeating) = 3/3 or 1

The problem is in infinite numbers, You technically can't do math on them because the calculation never stops.

I am editing myself to make more sense, well it all made sense to me, but nevermind.
Edit:

To even add 2 infinitely repeating numbers or multiple an infinitely repeating number, you have to make it finite. That is where the equation is changed. For the above examples:

when you multiplied 10 times .9 (repeating) that would take an infinite amount of time to calculate. Unless you make the system finite, thus changing the system.

The same goes for in my example adding .3 (repeating) and .6 (repeating) would take an infinite amount of time. So you make both numbers finite and change the system.

In both cases you would round the number so .9(repeating) would become 1. .3(repeating) would become something like .33333 and .6(repeating) would become .66667 - .3 and .6 would be rounded to the same place as they are in the same set. By rounding and making finite numbers our calculations work.

Posted: Thu Jul 19, 2007 7:53 pm

So - clearly - math is wrong.

Thank you, everyone. For I have just disproved mathematics.

**extreme pompousness*

Wink