Monty Hall

[EFLImpudence]

To clarify (or mystify) even further -

if those who know the answer should not tell then anyone who states the correct answer quickly is either very clever or a cheat and -

those who have not stated the answer either know, are very clever but afraid others will think them a cheat or are pretending they know but don't.

 

[JohnW2]

To clarify (or mystify) even further - if those who know the answer should not tell then anyone who states the correct answer quickly is either very clever or a cheat and - those who have not stated the answer either know, are very clever but afraid others will think them a cheat or are pretending they know but don't.

One could say those things

Seriously, though, there obviously has to be some trust. The relevent distinction is between those who know the answer because they have encountered the problem before (and maybe struggled and agonised before their Eureka moment!) and those who have never encountered, and therefore have never thought about, the problem before. If any of the latter work out an answer quickly, they obviously should post it immediately (and 'claim their prize', on trust of not having cheated!) - it's the former people who would 'spoil' things for others if they simply 'spewed out' the answer which they already knew.

In fact, the numerical answer isn't the issue - I suppose I could tell you that without 'spoiling'anything significantly. It would be your explanation of how that answer can be obtained which would matter

... and, of course, as with all these puzzles, Googling has to be 'banned' - since the answers (with explanations) are all over the place.

Kind Regards, John

 

[ebee]

Bloomin` `eck Mr Sheds, you started me on another now.

Today we went a walk in the country and there was a stream and a bridge and I started thinking about you asking that puzzle.
I was thinking about it whilst we stopped on a picnic table and got a slap around the head (well three generations - 8 people in the countryside & I`m weighing this puzzle up ).
LOL

PS I`m getting near to the answer.

 

[JohnW2]

PS I`m getting near to the answer.

Great - I suggest you concentrate on 'thinking', rather than calculating - once the Eureka moment has hit you, the easy way of getting the answer is very easy! However, it's still 'calculating' (no 'trick').

There is no secret about the 'less easy' way of doing it. If you just assign symbols to each of the variables (river speed, rowing speed etc.) and plod through the algebra, you'll end up with the correct answer - but it's better (and more intellectually satisfying) to try to avoid having to do that!

Kind Regards, John

 

[ebee]

Indeed, I know algebra will sort it (two farmers meet at crossroads, each with number of sheep - simultaneous equation) but have tried the pure thought route instead and got a bit further on.
Once I get the Eureka it will be simple.
Brain just needs a nudge.


Then of course it becomes a "Kickself question".

 

[EFLImpudence]

I haven't had a lot of time but I shall be honest and say I'm not not posting the answer because I knew.

 

[JohnW2]

... Once I get the Eureka it will be simple.
Brain just needs a nudge.

Indeed. Once you and others have had a grapple with it, if needs be I suppose there might be some clues.

I'm not sure if it counts as a clue, but I can tell you that there are any number of variants of this problem involving escalators, conveyor belts, treadmills and suchlike! (and some pretty close ones involving flies and trains!)

Interestingly, the question, as correctly worded by BAS, contains information which stops you using the same 'easy' approach as was applicable in the Hole-through-a-Sphere problem.

Kind Regards, John.

 

[ebee]

it clicked

 

[ebee]

Yes , the fly stopping a train is a good one

 

[ebee]

Mmm, clue or not?
Yes I can see what you are thinking!

 

[JohnW2]

Mmm, clue or not? Yes I can see what you are thinking!

The same principle applies with any of those 'moving substrates' - be they rivers, conveyor belts, trains or whatever.

Kind Regards, John

 

[DetlefSchmitz]

Ah - I woke up knowing the answer!

 

[JohnW2]

Ah - I woke up knowing the answer!

Well done - that's exactly how 'Eureka moments' often arise. It's a bit like finding obscure bugs in computer code. The amount of time expended in thinking/grappling/agonising is often almost random - one is probably as likely to 'see the light' 2 minutes into the exercise than after 100 hours. In fact, the longer one 'stares at' such a problem, the more difficult it probably becomes to 'think laterally' - so it's best if one is lucky and suceeds early!

As I wrote last night, there are countless variations of this 'moving substrate' sort of problem around (and, indeed, some real-word examples of the same concept) - so, having now 'seen this light' (assuming you have seen the correct light ), you should now be able to deal with any of the others with minimal effort.

Kind Regards, John

 

[echoes]

Funny how the problem seems so much simpler when the river and bridges are replaced with an aeroplane and 2 landmarks.

 

[JohnW2]

Funny how the problem seems so much simpler when the river and bridges are replaced with an aeroplane and 2 landmarks.

Does it? As I said, as far as I am concerned, the concept is essentially the same with any 'moving substrate' - I think I mentioned rivers, conveyor belts, escaltors and trains - but we can, indeed, add air (and plenty of other things) to that list as well However, the principle is the same for all of them.

Kind Regards, John