Author Topic: Riddles!  (Read 133612 times)

Offline yossig

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Re: Riddles!
« Reply #360 on: September 05, 2019, 11:33:59 AM »
If you want a much harder riddle try the same thing with 12 marbles. You still need to determine whether the odd one is heavier or lighter and you still get only 3 weighings.
can do this one in 4 times easy

Offline Yonah

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Re: Riddles!
« Reply #361 on: September 05, 2019, 01:30:55 PM »
can do this one in 4 times easy

But that's not the point :)

Here is my proposed solution - first split the 12 marbles into 3 groups of 4, let's call them A,B, and C. Then weigh A vs. B

There are two possibilities - if A and B are equal, then we know that the odd marble is in Group C. We take any 3 marbles from Group A+B and weigh them against 3 of the 4 in group C. If they are equal, the remaining group C marble is the odd one, and we weigh it against any other marble to determine if it's heavier or lighter. If the 3 from group C do not equal the other three = we know that one of those 3 is the odd one, we know if it is heavier or lighter, and we can weigh two of the three remaining marbles against each other to determine which is the odd one out

Here's the Tricky Part - say group A and B are not equal - for the sake of illustration, let's say A is heavier than B. Given this, we know the following:
- Group C are all the same weight
- If the odd marble is one from Group "A" it must be heavier
- If the odd marble is one from group "B" then it must be lighter.
- We then take 1 marble from Group "B"- let's call it B1 and combine it with any 3 from group C - we then weigh that marble against the 3 remaining marbles in group b, with one of the 4 from A - let's call that 1 A1.

So our Two Groups:
A1, B2, B3,B4
and
B1, C1,C2,C3

We know that C4 is not the odd one
We put A2,A3,A4 on the side - they are still unknown

Here are the possibilities:
- If the side with A1 remains heavier - we know that the marble is either A1 or B1. We weigh one of them against any other marble to find the odd one. If it's A1 then the odd marble is heavier, and if it's B1 then the odd marble is lighter
- If the side with A1 is lighter - we know that the odd marble is one of the three B's on that side, and that it is lighter - we weigh any two against each other to find the odd one out.
- If the two sides are equal, then one of  A2,A3,A4 must be the odd ones out, and the odd one is heavier - we weigh any two against each other to find the odd one out.



Offline Yonah

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Re: Riddles!
« Reply #362 on: September 09, 2019, 12:46:32 PM »
This is driving me nuts. Any ideas?

https://twitter.com/jessmisener/status/1166448813931974660

They posted the official answer, I had the right doors, but wrong logic:
https://www.npr.org/2019/09/08/758703217/sunday-puzzle-gs-l-s

Quote
Challenge answer: The correct door is the one between the M and the H. If you write the word OUT between M and H, you get the word MOUTH. The puzzle said "Only one door provides an opening," which is what a mouth is. And a door with OUT written on it should naturally be an exit.

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Re: Riddles!
« Reply #363 on: September 09, 2019, 12:53:42 PM »
They posted the official answer, I had the right doors, but wrong logic:
https://www.npr.org/2019/09/08/758703217/sunday-puzzle-gs-l-s

I think it is more that you used logic while they did a stupid play on words in the question which makes no sense.
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Offline yitzgar

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Re: Riddles!
« Reply #364 on: September 09, 2019, 01:15:01 PM »
The riddle was worded in such a way that one would have assumed that there was a logical exit, not just a play on words.

Offline stooges44

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Re: Riddles!
« Reply #365 on: September 09, 2019, 01:19:18 PM »
The riddle was worded in such a way that one would have assumed that there was a logical exit, not just a play on words.

+1
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Offline Yonah

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Re: Riddles!
« Reply #366 on: September 09, 2019, 01:37:38 PM »
Another oldie but goodie that I'm sure most of you have heard:

The givens:
-There is a group of 4 people who need to cross a bridge
-It's dark, and there is only 1 flashlight, and it's needed to cross the bridge
-Only 2 people can cross the bridge at one time
-If you walk the flashlight across, someone will need to walk it back for the next group
-The 4 people each have a different max speed, in minutes, to cross the bridge - 20,15,10, and 5 minutes respectively
-The bridge is too long for the flashlight to illuminate the far side from one end, and it's to treacherous to walk n the dark.

What is the fastest time you can get all 4 people across the bridge, and what sequence do you use? (Hint, the time answer is always the same, but there is more than one valid sequence)




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Re: Riddles!
« Reply #367 on: September 09, 2019, 02:29:22 PM »
65?
Workflowy. You won't know what you're missing until you try it.

Offline whYME

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Re: Riddles!
« Reply #368 on: September 09, 2019, 02:42:04 PM »

Offline whYME

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Re: Riddles!
« Reply #369 on: September 09, 2019, 02:46:58 PM »
Another oldie but goodie that I'm sure most of you have heard:

The givens:
-There is a group of 4 people who need to cross a bridge
-It's dark, and there is only 1 flashlight, and it's needed to cross the bridge
-Only 2 people can cross the bridge at one time
-If you walk the flashlight across, someone will need to walk it back for the next group
-The 4 people each have a different max speed, in minutes, to cross the bridge - 20,15,10, and 5 minutes respectively
-The bridge is too long for the flashlight to illuminate the far side from one end, and it's to treacherous to walk n the dark.

What is the fastest time you can get all 4 people across the bridge, and what sequence do you use? (Hint, the time answer is always the same, but there is more than one valid sequence)

I think you messed up with the times for each person. I don't think it's supposed to be so simple/straightforward.

Online skyguy918

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Re: Riddles!
« Reply #370 on: September 09, 2019, 02:55:26 PM »
55

<5&10
>5
<15&20
>10
<5&10

10+5+20+10+10=55

The times don't matter. If it's A<B<C<D, the answer will be something along the lines of A+3B+D.

ETA: Different exact amount of time here, but the principle holds - https://en.wikipedia.org/wiki/Bridge_and_torch_problem.

Offline Yonah

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Re: Riddles!
« Reply #371 on: September 09, 2019, 03:02:58 PM »
55

<5&10
>5
<15&20
>10
<5&10

10+5+20+10+10=55



The times don't matter. If it's A<B<C<D, the answer will be something along the lines of A+3B+D.

ETA: Different exact amount of time here, but the principle holds - https://en.wikipedia.org/wiki/Bridge_and_torch_problem.

55 is the correct answer, and there are two ways to do it - the way you described or
<5+20
>5
<5+15
>5
<5+10

Is also 55 minutes

I think you messed up with the times for each person. I don't think it's supposed to be so simple/straightforward.

I think so too - I think there needs to be a broader gap between the two faster and two slower people.

Online skyguy918

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Re: Riddles!
« Reply #372 on: September 09, 2019, 03:13:52 PM »
55 is the correct answer, and there are two ways to do it - the way you described or
<5+20
>5
<5+15
>5
<5+10

Is also 55 minutes

I think so too - I think there needs to be a broader gap between the two faster and two slower people.
Didn't notice that. Yes, it's supposed to be designed such that the fastest person ferrying the other 3 across is slower than the other solution.

Offline Yonah

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Re: Riddles!
« Reply #373 on: September 09, 2019, 03:14:11 PM »
A riddle (this one is actually based on a true story that happened to me early in my career):

You are a software developer for an e-commerce website. One Monday morning, the warehouse manager complains that there is a bug in the system. You've designed your software so that order numbers are sequential - i.e. 1,2,3, etc, but he claims that over the weekend, a handful of orders got order numbers out of sequence. He's concerned that with Black Friday coming up in a few weeks, that this is indicative of a bigger problem that might surface during the holiday shopping season, and a code release too close to holiday might cause other problems to crop up - obviously he wants it fixed immediately.

Some of your advance techs have looked at it, and can't find any problems with the orders except that the order numbers were out of sequence. They also tell you that this bug was limited to about 1 hour on Saturday night, but they can't find the source. But all of the orders received before and after appear to be fine and in the correct sequence.

You laugh at them, and tell them it's not a bug, and you know exactly why it happened.

What's the explaination?

Offline Yikes2179

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Re: Riddles!
« Reply #374 on: September 09, 2019, 03:19:07 PM »
Switching from DST caused some orders to be out of order

Offline Definitions

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Re: Riddles!
« Reply #375 on: September 09, 2019, 03:21:37 PM »
Switching from DST caused some orders to be out of order
+1
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Re: Riddles!
« Reply #376 on: September 09, 2019, 03:23:26 PM »
They posted the official answer, I had the right doors, but wrong logic:
https://www.npr.org/2019/09/08/758703217/sunday-puzzle-gs-l-s
A good riddle is one in which you harbor no ill feelings against the person who asked it to you when you learn the answer. I can't say this fits that category.
« Last Edit: September 09, 2019, 04:23:56 PM by YitzyS »

Offline whYME

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Re: Riddles!
« Reply #377 on: September 09, 2019, 03:47:05 PM »
I think it is more that you used logic while they did a stupid play on words in the question which makes no sense.
My first thought when I saw this solution was "this belongs on a Laffy Taffy"

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Re: Riddles!
« Reply #378 on: September 09, 2019, 04:37:03 PM »
Another oldie but goodie that I'm sure most of you have heard:

The givens:
-There is a group of 4 people who need to cross a bridge
-It's dark, and there is only 1 flashlight, and it's needed to cross the bridge
-Only 2 people can cross the bridge at one time
-If you walk the flashlight across, someone will need to walk it back for the next group
-The 4 people each have a different max speed, in minutes, to cross the bridge - 20,15,10, and 5 minutes respectively
-The bridge is too long for the flashlight to illuminate the far side from one end, and it's to treacherous to walk n the dark.

What is the fastest time you can get all 4 people across the bridge, and what sequence do you use? (Hint, the time answer is always the same, but there is more than one valid sequence)
You gotta make it more dramatic!

I heard it like this:

There were four people stuck on a boobytrapped island, which will blow up in exactly 17 minutes. There's a rickety bridge off the island, but that will also blow up in 17 minutes. it takes the people 1, 2, 5, and 10 minutes... etc.

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Re: Riddles!
« Reply #379 on: September 09, 2019, 08:17:45 PM »
You gotta make it more dramatic!

I heard it like this:

There were four people stuck on a boobytrapped island, which will blow up in exactly 17 minutes. There's a rickety bridge off the island, but that will also blow up in 17 minutes. it takes the people 1, 2, 5, and 10 minutes... etc.
Heard it the same way from here
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