I have some train tracks very close to my house . Everyday I go down to the tracks and wait for a train to pass. There are two types of train – passenger trains and freight trains. I have been going down to see the trains at random times for a few months now and 90% of the time I see a passenger train. So far, so what?
Well, the other day I met the man in charge of the line, and he told me that 50% of the trains on the line are passenger trains and the other 50% are freight trains.
How can this be the case?
As ever, please do NOT post your answers, but feel free to say if you think you have solved it and how long it took. Solution on Monday.
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August 27, 2010 at 5:29 am |
Think I got it,
time 30 sec aprx
August 27, 2010 at 5:38 am |
Solved it halfway through reading the first paragraph.
August 27, 2010 at 5:39 am |
I think I’ve got it also – time approx 10 seconds
August 27, 2010 at 5:39 am |
My question is this why are they allowed to pollute the air, surely there are cleaner forms of fuel. How often does the engineer ware that red shirt with his overalls and who are the two other people with him? Isn’t that distracting as they look like girls or children? You work on those and I’ll work on the %…..hehehe…..I want t savory this Friday’s puzzle!
August 27, 2010 at 5:51 am
Oh, wow I’ve just thought of several ways to work this after reading it again carefully…hmm wonder if I got the right approach to this….a couple of minutes but may be a tricky one? I’ll keep thinking and not rush to an answer yet….
August 27, 2010 at 7:16 am
If I remember correctly, the cloud you see on steam trains is… vapor… water. Of course, there must be some form of water heating, but that’s not the main source of the “smoke”.
August 27, 2010 at 8:28 am
Steam train. I’m sure there’s a clue in the name there somewhere.
August 27, 2010 at 8:46 am
looks like coal……booo! but really just a side distraction…..lol… can’t you see the sheep?
August 27, 2010 at 9:24 am
Don’t be mistaken by the name. Yes, steam train, but the steam is more or less in a closed cycle(actually rather less closed, but ideally it would be). What’s coming out of the chimney is smoke from the coal or wood fire that’s used to heat the water.
August 27, 2010 at 10:29 am
As I said, I might be wrong.
But a close cycle needs to refrigerate water so that it can contract and be used again in an expansion cycle. It is the curse of the thermodynamic processes that there are no perfect process of conversion between thermal and mechanical energy. You can convert it but in the process there must some cold source which must became a little warmer. A train simply has no way to do that indefinitely. Instead it relies on the atmosphere to do that, releasing the vapor. That’s why we see water deposits near old steam trains lines, to replenish the water lost, and also why, the vapor comes out of the train chimney in pufs… the smoke beat is marked by the expansion cycles the steam suffers to push the pistons.
August 27, 2010 at 12:55 pm
I don’t want to be rude, but if you don’t know what you’re talking about, please do some research before posting! Wikipedia has a very complete page about stream locomotives: http://en.wikipedia.org/wiki/Steam_locomotive
You can learn that almost all locomotives are in open cycle, and the steam and exhauts gases are combined before being released, explaining the puffs. And you can know for sure that if the smoke is black, it’s obviously not just steam!
August 28, 2010 at 12:57 am
You don’t want, but you are rude. I was commenting a commentator who said the cycle was closed and “What’s coming out of the chimney is smoke from the coal or wood fire that’s used to heat the water”. I said the cycle is open (the steam goes to the atmosphere) and the main source of the “smoke” is water valor (never said it is only vapor). You confirm what I said, so, explain to me, why should I deserve the tone “if you don’t know what you’re talking about, please do some research before posting!”. Where did I fool anyone to deserve that treatment? Even if I was wrong, which I were not, I was careful to warn it was things of memory and reasoning, which I think particularly appropriate to a puzzle’s column. Do you Google your answers to the puzzles?
Of course, you might be referring to Rapax, which I think was wrong, but respect enough to think he might be right. But either to him or to me, wrong or right, neither of us deserves that statement of yours, not here which are usually a gentle place to stay and talk. Rude, indeed!
August 28, 2010 at 7:35 am
@Joao Pedro. Some of us enjoy the pleasant chat & exchange of ideas. So thanks for that!
August 29, 2010 at 12:00 am
Thanks for your support, @Rusty.
There’s something I said, that’s been gnawing at me. I said
“the cloud you see on steam trains is… vapor… water. Of course, there must be some form of water heating, but that’s not the main source of the “smoke”.
There’s an implicit admission there that there are other gases in the “smoke”, but how can I vow they are not the main part of it? The statement above was either intuition or memory, but I was worried it could be untrue. The main argument in my intuition was the beating the smoke: it doesn’t came continuously, but in rhythmic shots, which suggests the valves discharging the steam. But this is a weak argument, as the steam discharge could be used to drag the exhaust gases.
In the end, I think I didn’t need to be worried about what I wrote. A simple fact I forgot: exhaust gases from good combustion are invisible. If the combustion is done well, the result gases are mainly CO2 (good Coal) and maybe water (worse coal or Wood). CO2 is “transparent”. Is famous now for its absorption in the Infra-red (hot house effect), but not in the visible range. Water in the gas state is also transparent (the same way) but there is a trick here: when it pushes against the pistons, it converts a lot of its thermal energy into mechanic, and looses temperature. The steam out of the chimney is then above the atmospheric vapor pressure for its temperature, and condenses in a visible cloud. Yes, that cloud might be dirty, but only if the combustion is not complete and ashes are carried way to the chimney… an undesirable effect. So the answer is simple: yes, water vapor is indeed the majority of what we see, because the rest is invisible.
August 30, 2010 at 4:56 am
Wow all of you busy while I was gone?…lol….boy those sheep sure can get things stirred up….
August 27, 2010 at 5:45 am |
There are dozens of possible answers. I’ve come up with 4 very plausible in under 2 minutes. I would hope for more guidance in the question as to what type of answer is required.
August 27, 2010 at 6:45 am
I agree. There are too many interpretations possible.
August 27, 2010 at 6:52 am
A well, I think I found the answer Richard was looking for. One of the interpretations tends to be much more realistic than the others, although I still know about 3 other solutions.
August 27, 2010 at 5:51 am |
I agree with Morgan. I’ve got an answer that’s logical, but also very very easy. Am I the only person who can see an angry-looking Scots terrier in the smoke?
August 27, 2010 at 5:58 am
I too can see the angry doggy.
August 27, 2010 at 6:02 am
I see him! Maybe it’s another “How many faces” puzzle?
August 27, 2010 at 6:10 am
@ Martha I sort of see that terrier but what I first saw was a very angry neurotic sheep with over-grown coat of wool!! One must of got loose!
August 30, 2010 at 5:06 am
OMG it is progressive….these faces we see….I turned on and booted up my lap top and when my screen saver a photo of giant redwood forest…. came up and suddenly I see dozens of faces looking back at me!
August 27, 2010 at 5:57 am |
I think I got it! 30 secs-ish. Have also thought of a more unlikely way.
August 27, 2010 at 5:57 am |
[...] It's the Friday Puzzle! « Richard Wiseman's Blog [...]
August 27, 2010 at 5:58 am |
I’ve got it.
August 27, 2010 at 6:00 am |
Much too easy. Either that or I’m wrong!
August 27, 2010 at 6:03 am |
I don’t like this puzzle. I know what the answer is supposed to be, but it’s silly. I can easily come up with a number of other plausible answers.
August 27, 2010 at 6:05 am |
I don’t like this puzzle. I know what the answer is supposed to be, but it’s silly. I can easily come up with a number of other plausible answers.
P.S. It’d be nice to be rid of these incessant spam comments…
August 27, 2010 at 6:08 am |
I can think of an answer or two, but they’re all stupid and probably not what you’re intending.
August 27, 2010 at 6:13 am
those might be the right ones or so seems we are thinking the same thing….lol….
August 27, 2010 at 6:19 am |
Is the answer related to Harry Potter?
Thats all I´ve got….
August 27, 2010 at 6:23 am |
Just a comment on an observation……over the last few Friday puzzles on one has had to die! Wow! No one to choose pet over child or other such life or death decision…..hmmm……may be Richard just needs to get a little closer to the train track to get a better view…..he may have not been able to see clearly……. he he he….
August 27, 2010 at 6:26 am
drat it those bad typos!!! *no one* not *on one*
August 27, 2010 at 6:34 am
Ha ha!
August 27, 2010 at 6:37 am
Hello Rusty…. now what image came to you first?….lol…..
August 27, 2010 at 6:43 am
Hi Lila. How come you can see right through me when I’ve said so little on here!!! I take it you’re talking BBQs? [Note to self: Must learn to be less transparent].
August 27, 2010 at 8:06 am
@Rusty I can see a really nice grill in that photo…..lol…..
August 27, 2010 at 8:17 am
Ooooh errrrr Mrs!
August 27, 2010 at 8:56 am
Oh ooohhh ….lol….oopss…..oohh…..uuuhhhoooo….oh my goodness……lol……OK….lol……haha….hehe…..got it….slap to head….
August 27, 2010 at 9:04 am
them wasn’t no Freudian slip……lol….it’s {it is} 5am my time and no sleep yet…..and that’s {that is….hehehe} my storey and I’m {I am} sticking to it!
August 27, 2010 at 6:25 am |
After God created the Earth in 6 days, he had a little rest, what isn’t so well documented is that during his “rest” day, I paid him a visit and showed him this Friday puzzle…… God thought long and hard, but couldn’t figure out an answer. So at the beginning of the 2nd week of creation I gave God the answer I’d come up with, thus proving the fallibility of imaginary deities…..
August 27, 2010 at 6:57 am |
Assuming that the freight trains aren’t invisible or something silly like that, and that the “randomly” timed visits are truly random throughout time, there are a couple of plausible explanations I can think of in about 30s. Not sure that they are right though as the question doesn’t quit contain enough information to be certain but implies that something which would need to be true is.
August 27, 2010 at 7:08 am |
Lovely puzzle. I’ll risk to say that Richard is not very clear how he conducts his observations, so, depending on how he is doing, there are two explanations. But, it is still a lovely puzzle.
(Now, let’s what the others wrote)
August 27, 2010 at 9:12 am
@Joao Pedro do you see one of them sneaky sheep hiding in the above photo? I see one in the smoke….they are more than what we thought….they can turn themselves into smoke or astral projection …that must be why they don’t mind the restricted space in those pens…..they may need to have some sort of force field around them…..
August 27, 2010 at 10:43 am
Wow, you are right! That smoke looks a lot like wool. I think I was wrong in my identification: this is not a steam train but a sheep train. It uses wet sheep and works by drying the wool until it became fluffy and expanded. The greater volume then serves to work against pistons and move the train. I guess we can wet again the sheep in an almost closed cycle, but the train in the photo appears to be old, and not that sophisticated. It simply launches the sheep overboard through the Chimney.
I heard that Afro wig trains are more efficient but people objected about the color of the smoke, and sheep is a nature thing… no one objects to this kind of pollution.
PS.: I thought in one more way of observing the trains, so, now I have one more solution. I hope I don’t forget them until Monday. And there is also a fourth, the most simple solution of all, able to be resumed by a simple 4-letter word.
August 28, 2010 at 11:23 am
@Lila, are you still being watched by PETA? Be careful, I think my sheep train idea is not to their liking (although a very fluffy sheep shot from a chimney is well cushioned by its wool when it lands).
By the way, did Richard changed his text? I don’t remember to read yesterday morning this part “and wait for a train to pass”. If that’s so, the observation model I was assigning to Richard is pruned of two possibilities, and my solutions are reduced to two.
For the record, the other possibilities I was considering before read that was “I didn’t wait”, and “I wait for a certain fixed time”. Thinking better, my initial solution for the last case, was wrong.
August 30, 2010 at 5:13 am
@Joao Pedro I went back and looked and I don’t remember if it did or not, but for me it won’t change mt answer…..we shall see soon!
August 27, 2010 at 7:34 am |
Pretty sure I have this roughly. I haven’t bothered to figure it exactly to give the 90% observed, but the principle….oh hang on, got it exactly now.
August 27, 2010 at 8:14 am |
I got the answer immediately. But I don’t know if it is meant to be THE answer. Still, it’s definitely the answer Ockham prefers.
August 27, 2010 at 2:42 pm
Oh, no, I missed a small detail.
None-the-less, after rereading the puzzle, I got the answer immediately.
August 27, 2010 at 8:51 am |
One explanation immediately (~ 2 secs). After reading the comments and the question again, another plausible explanation.
August 27, 2010 at 8:57 am |
Thought of a possible answer right away.
August 27, 2010 at 9:06 am |
I guess it is obvious so it took me no time at all.
August 27, 2010 at 9:16 am |
I’ve thought up of two alternative answers – one is based on walking down to the line every *day*, the other is based on distinguishing between engines and traffic.
August 27, 2010 at 9:18 am |
Think I’ve got it.
August 27, 2010 at 9:37 am |
No time at all, it’s very similar to a puzzle I have seen before. Think it was a Martin Gardner. In that case, boy took one of 2 subway routes to one of 2 girlfriends depending on which train came first and spent 80% of his time with one girlfriend.
August 27, 2010 at 9:46 am |
I solved it, I think…
August 27, 2010 at 9:57 am |
As many others have noted, it seems like many different solutions are possible. However, I think I can see the intended solution.
August 27, 2010 at 10:12 am |
There is one obvious answer, but I have that hollow feeling inside that says I have missed something…
some of the people here are very clever.
I always thought I was pretty smart, but…
Obviously not that smart.
From now on, my post on Fridays will be ’30 secs. Got it. Dead easy’.
Not hard to type, is it?
(Not that anyone would lie, or anything…)
lol
Honestly, just joking.
August 27, 2010 at 2:13 pm
Oh dear, I am actually quite stupid.
It has come to me (in a puff of smoke? Or steam? Or maybe a combination of the two?)
So it took me approximately 6 hours and repeated readings.
That is disarming honesty for you.
I know that my answer is correct and the only real answer.
I had an inkling before, but this one is so much clearer.
Goodbye from cloud cuckoo land.
August 27, 2010 at 10:23 am |
20 secs, hope I got it right.
August 27, 2010 at 10:58 am |
Random.
And yep, I can see that angry looking terrier in the smoke, haha!
August 27, 2010 at 1:36 pm |
Got it without reading the clue — or even visiting Richard’s blog — in about 1/100 of a second, and most of that time was spent checking my math and putting a new transmission in my Volvo.
August 27, 2010 at 1:43 pm |
Methinks there is one little 3-letter word missing from the problem that would clear this all up and make me sure that I’m right. A small clarification on the definition of one of the words (related to the missing word) is needed. Maybe it’s a British / Canadian distinction…
August 27, 2010 at 2:33 pm |
Yea, I think I got this one!!
Unfortunately, it came so quickly to me, seconds after reading, that I think I must be wrong.
August 27, 2010 at 2:56 pm |
Came up with a plausible answer in about 2 seconds.
August 27, 2010 at 3:02 pm |
It has occured to me that maybe the puzzle is supposed to be really simple to solve and that the real excercice from this puzzle is to see how many feel insecure when finding the answer right away.
August 27, 2010 at 3:14 pm |
I hope all these posters give their answers on Monday (especially the ones who can think of half a dozen possible solutions). What a cop-out if everyone says ‘yep, exactly what I thought’! Incidentally, my first answer was wrong, but I’ve got the right one now. (I originally missed the words ‘at random times’ and assumed he was going at roughly the same time each day.)
I think it would help, though, if it’s made clear whether he’s going down because he’s a trainspotter, or because he wants to cross the line to get to the shops.
August 27, 2010 at 4:11 pm |
Pretty quickly, I could think of a lot of silly ad hoc scenarios.
Took me a few minutes to figure out something, that adds no further information to the story.
August 27, 2010 at 4:51 pm |
I’ll formed question, or perhaps too open ended thus too many plausible explanations.
August 27, 2010 at 4:58 pm
For example, when he goes down to the train tracks how much time does he spend there 1 minute -> all day? Also what is the frequency of the trains, every 1 minutes -> once a day? I’m sticking with this was an ill formed question, but I do have a plausible answer – based on assumptions to those two questions. Answer took about a minute.
August 28, 2010 at 2:24 pm
I believe the “right answer” is independent of those two questions. Could wait anytime from 1 min to 23h 59m, trains could run from 1 per minute to 1 per day, and the general solution still applies.
August 27, 2010 at 6:15 pm |
I have an answer but it’s wrong because people aren’t supposed to do that and it still wouldn’t change the train.
August 27, 2010 at 7:03 pm |
there are so many ways to answer this
August 27, 2010 at 7:24 pm |
Easy, 0.1 picosecond
August 28, 2010 at 12:07 am |
may be half of 0.1 picosecond.
i already solved it.
August 28, 2010 at 12:11 am |
[...] It’s the Friday Puzzle! I have some train tracks very close to my house . Everyday I go down to the tracks and wait for a train to pass. [...] [...]
August 28, 2010 at 1:34 am |
I remember seeing this puzzle in one of the 1957-58 editions of the Scientific American. I believe it was one of Martin Gardiner’s (spelling?).
August 28, 2010 at 5:02 am |
I solved it so fast that I’m almost sure that I’m wrong.
August 28, 2010 at 7:46 am |
Oooh. I’ve just thought of two more answers. But if the “random times” are truly random, only my first answer is correct.
August 28, 2010 at 1:56 pm |
If I’m right then instantanious.
August 28, 2010 at 3:37 pm |
Already knew it.
I originally heard this in a puzzle book — possibly by Martin Gardner — where the problem was stated something like this:
Joe has two girlfriends. One lives in Brooklyn, the other in The Bronx. He loves them equally and doesn’t want to slight either, so when he feels like visiting one, he lets fate decide which one: he goes to a subway station where two train lines stop, one going to Brooklyn, the other to The Bronx. He takes whichever train comes first. Both trains run every ten minutes, and yet he finds himself in The Bronx 90% of the time. Why?
August 28, 2010 at 6:44 pm |
how is this NOT the most obvious puzzle ever
August 28, 2010 at 7:20 pm |
“Me” is correct, this is included in that variant in Martin Gartner’s ‘best puzzles’ booklet, I read it two days ago.
August 28, 2010 at 9:29 pm |
A good clue is that “tracks” is plural.
August 29, 2010 at 12:11 am |
Frieght trains usually run at night when you’re asleep. Duh.
August 30, 2010 at 1:21 am
You shouldn’t post what you think is the answer till he posts the answer,
and I think I got it in about 20 seconds after I finished reading it.