I have 45 socks in my drawer. There are 14 identical blue, 24 identical red and 7 identical black. Yesterday all of the lights went in my house, so now I live in complete darkness. How many socks do I need to take out of the drawer to ensure that I have a pair of each colour?
As ever, please do NOT post your answer, but do say if you think you have solved it and how long it took. Answer on Monday!
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December 17, 2010 at 5:34 am |
Solved it via brute force in about 30 seconds.
December 17, 2010 at 5:40 am |
Here, borrow my torch.
December 17, 2010 at 5:43 am |
Took me about about 30 seconds.
December 17, 2010 at 5:58 am |
Taking all of them out of the draw will ensure that you have a pair of each…
December 17, 2010 at 2:37 pm
But that’s not how many you NEED to take out to do so. The puzzle specifically asks how many socks you “NEED to take out,” so the solution requires coming up with the minimum number of socks.
December 17, 2010 at 7:45 pm
As there’s an odd number, not all will be paired.
December 17, 2010 at 6:06 am |
But all socks look grey in the dark
December 17, 2010 at 6:13 am |
thought in terms of doing it by brute force and then decided there were too many options. Then thought what is the worst case scenario – and the opening scene of Rosencrantz and Gulderstern are Dead went through my mind – I jotted three numbers down and … got an answer – I don’t however feel confident about it.
December 17, 2010 at 6:24 am |
Why have you got so many red socks? Are you a cardinal?
December 17, 2010 at 6:32 am |
It just took the time to read got the answer in about negligible say 1 second time. For the first time feeling happy about it..
December 17, 2010 at 6:34 am |
Are you looking for the worst case solution?
December 17, 2010 at 1:07 pm
“ensure”, so yes.
December 17, 2010 at 7:04 am |
I came up with two ways but one I’m sure would be called cheating…..about the length it took to read question and a minute to think it through…..my question is why 7 black socks? Is it customary to substitute an unmatched sock with a black sock?
December 17, 2010 at 7:05 am |
Did your lights really go in, or was that a typo?
December 17, 2010 at 7:35 am
No, lights go i.e. stop working. And they can go in a house, in a car or on a plane.
December 17, 2010 at 9:53 am
cute!
December 17, 2010 at 7:33 am |
Pretty easy I think, about 30 seconds…but you still must select two to put them on!
December 17, 2010 at 7:54 am |
Got it after a few seconds. As always, carefully reading the question is key.
December 17, 2010 at 7:57 am |
Well that seems blindingly obvious. So there’s probably a catch that I’ve missed.
December 17, 2010 at 8:06 am |
That was also easy, just 15 seconds.
December 17, 2010 at 8:16 am |
Too easy? Or maybe I’m just a freakin genius?
Yeah, ive probably missed something.
I bet the sock in the picture was commissioned by some bloke who appears on the been to explain the financial sector.
December 17, 2010 at 8:21 am |
Very confusing… not mentioned of arrangement of socks… is it stacked one above the other? or scattered or three colors socks stacked and kept separately.. but got some answer with one assumption
December 17, 2010 at 8:21 am |
I could solve the problem by the time I finished reading it. No complex mathematics is called for. However, if you want a pair of each of three colors with total certainty, you would end up taking out nearly all. So, why not save the trouble and take out all.
December 17, 2010 at 8:31 am |
Started jotting the numbers down, then realised the obvious. So about a minute
December 17, 2010 at 8:33 am |
Solved it in about 1.5 seconds…..
December 17, 2010 at 9:07 am |
A very short time to work out (< 15s) – I like the variation of "a pair of each colour".
December 17, 2010 at 9:11 am |
The sock in the picture is a Paul Smith I think.
I got it in under a minute, unless I’m missing some clever trick.
December 17, 2010 at 9:13 am |
Indeed, here is the sock: http://tinyurl.com/2w9opal
December 17, 2010 at 9:28 am |
About 5 seconds, answer seems mildly unintuitive compared to similiar puzzles I’ve seen in the past, but otherwise pretty straightforward.
December 17, 2010 at 9:44 am |
Solved it in a few seconds. You’d probably be better lighting a torch than carrying around all of those socks.
December 17, 2010 at 9:56 am |
I’ve worked it out and am quite confident.
However an easier solution would be to pair the socks BEFORE putting them away that way you won’t have a problem finding a pair again!!
December 17, 2010 at 9:56 am |
Answer seems to easy so am not sure 15 secs
December 17, 2010 at 10:18 am |
Ive not worn an identical pair of socks for 4 years.
December 17, 2010 at 10:18 am |
I re-read the question and ended up doing it twice, since I added the wrong way the first time. I’m pretty sure I’ve got the right answer this time, unless I’ve missed something blindingly obvious.
December 17, 2010 at 10:20 am |
I’m surprised why no-one’s questioned why he’s only got 7 black socks – did the other member of the fourth pair get lost in the wash?
I’ve seen similar puzzles before, and there’s bound to be a simple solution, but I used brute force probability.
December 17, 2010 at 12:09 pm
Hey Mittfh, I noted that there are only 7 and asked if a black sock will match anything? Like one red and one black can stand in for the missing red sock….oh but that could lead to all kinds of other options…hmmm…gotta study this idea….
December 17, 2010 at 3:40 pm
In fact one year ago, Richard had 7 complete pairs of black socks and was in the same situation. Even with double as much black socks he had to grab as much socks as this time to ensure that he had one pair of each colour!
December 17, 2010 at 10:30 am |
took seconds. using brute force probability
December 17, 2010 at 10:31 am |
I think I know the answer. I took me maybe 2 seconds.
December 17, 2010 at 10:56 am |
two minutes – started at the wrong end of the puzzle then realised and started again then it took 30 seconds
December 17, 2010 at 11:07 am |
Soved in about 1 min total. But I had to read it twice. After the second reading it took me 3 sec.
December 17, 2010 at 11:10 am |
Er – about 3 seconds today!
December 17, 2010 at 11:53 am |
Easy: use your cell phone to light the drawer up.
December 17, 2010 at 12:13 pm
@DeepField….much better idea than my first one to catch a jar of fire flies to light the drawer….lol…
December 17, 2010 at 12:57 pm |
Strange to see that some use probability to solve this problem: probability
is about measuring uncertainty, and we need to be certain that we have one pair of each color.
December 17, 2010 at 12:58 pm |
The traditional version of this puzzle asks how many must I take to ensure I have at least one matching pair – I guess the idea is that you take them to work and then put them on. This one is different because you want to get a pair of each colour. As is often the case with these puzzles, it isn’t made clear why the restrictions are imposed. So, let’s imagine you’re going away for three nights and you want to be sure you don’t wear the same colour any day. If I’ve got the answer right, you’ll be bringing back a lot of unworn socks just for the sake of avoiding repetition.
December 17, 2010 at 1:09 pm |
Took a fraction of a second.
December 17, 2010 at 1:22 pm |
A few seconds, using subtraction.
The Friday puzzles seem to be getting easier.
December 17, 2010 at 2:18 pm |
Use a flashlight? save a lot of trouble.
December 17, 2010 at 2:28 pm |
Poor management!! Why on the earth you keep so much pairs of the so many similar colours in the same drawer and mi them up to later get into the trouble? What I do is to keep the one socks into the other and I need to pick up a single socks, and the pair is with me, lights or no lights.
December 17, 2010 at 2:37 pm |
These questions are too easy, I am the best, it took me 5us to read the question and I had already formulated the answer before I finished reading the question.
Oh, right, a bunch of you j$rks already beat me to that response.
December 17, 2010 at 2:40 pm |
About 2 minutes, then Bing! So easy when you realize it!
For all of those using math and probabilities, think about it again…
December 17, 2010 at 2:43 pm
Oh, a pair of *each*, oops, I thought it was just one pair of any kind. Hmm, must think about it again!
December 17, 2010 at 2:42 pm |
Took about 60 seconds. I’m interested to know if the people who got it virtually instantly were correct and if they are very quick at basic arithmetic (or perhaps my method is completely wrong).
December 17, 2010 at 4:49 pm |
took me 20 seconds
December 17, 2010 at 5:14 pm |
even less than a minute!!!
December 17, 2010 at 5:28 pm |
I believe I solved it in a little over a minute. Had to re-read the question a few times.
Mike.
December 17, 2010 at 6:26 pm |
First i thought “oh no…”. Then, on the second try, it was easy. But im not sure im right.
The goal is, to find out, the minimum of Socks taking out, to have three pairs, one blue, one red and one black ?
December 17, 2010 at 6:41 pm |
Too many glasses of wine to even an attempt at the answer to be honest. In fact just reading it give me a headache
December 17, 2010 at 6:59 pm |
about 15 seconds
December 17, 2010 at 7:23 pm |
Under a minute here. Nice puzzle.
December 17, 2010 at 7:37 pm |
But surely you organise your sock drawer by colour, no? I don’t but it would be tricky coz some of my socks have pictures of cows on. Could you not open the curtains?
December 17, 2010 at 7:41 pm |
I think the answer depends on whether you interpret the information as 45 pairs of socks or 45 individual socks. I always pair my socks before I put them in the drawer so I first assumed it was 45 different pairs of socks. Re-reading the question I think it means 45 individual socks, which only makes a very slight difference to my answer.
December 17, 2010 at 7:51 pm |
Got the answer, double-checked the math and composed a minor symphony all before the page finished loading. Ta-da!
December 17, 2010 at 8:09 pm |
Solved it in about 15 or 20 seconds.
December 17, 2010 at 8:36 pm |
Couple of seconds
December 17, 2010 at 10:03 pm |
Easy problem…
If it had asked to ensure the result only a certain percentage of the times, it would have be much more difficult.
December 17, 2010 at 11:32 pm
Hello there Joao Pedro! I’ve been in the hospital for a while and missed my Friday Puzzle. Then my lap top was hacked while I was gone but now up and running again. Did I miss FE Dragon’s awesome puzzle?
December 17, 2010 at 11:09 pm |
Old old puzzle, so I knew the answer right away.
December 17, 2010 at 11:44 pm |
Look under the christmas tree. I’m sure you’ll find some there.
December 18, 2010 at 12:11 am |
[...] It’s the Friday Puzzle! I have 45 socks in my drawer. There are 14 identical blue, 24 identical red and 7 identical black. Yesterday all of [...] [...]
December 18, 2010 at 1:26 am |
I’m going to have a little ramble. Excuse me while I do so.
First off, I really hate clicking on the Friday puzzle, because you can bet the dollar that sits at the very lowest point anywhere in the world, the first person to post will say
‘Easy, didn’t have to think, 1min/less than a min/30 secs tops’ (delete where applicable.
THEN it turns into some sort of geeky bragging rights war.
’20 seconds, why are you spilling this rubbish out Richard?’
‘GOT IT IN 19s!!!! WOOO GO MEEEEE ‘
’5 seconds. And I think that the last person has some serious issues with their CAPS LOCK!’
‘I heard this when I was a baby in my mothers womb, I remember hearing her granda whisper it in her ear, so I think I can top you by saying – I got it before I was even born!!!!’
Well GO you.
I’m sorry, but do any of you actually sit there with a blooming stopwatch and REALLY time yourselves? I cast doubt upon that, and methinks Mr Wiseman, THAT if you sat some of these people down in a room and timed them with one of these (Don’t get me wrong, a lot of these are old school, sometimes with an added twist) Friday puzzles, half of them would scarper to the loo and claim diarrhoea as their consul.
Moving on, and I address you now Mr Wiseman, I did your willpower test, and I admit I did fail, I filled in my forms with complete honesty, yet I was dismayed that there was not an option for filling out the form for ‘I failed because I completely forgot I was doing this experiment because none of the options given to give up, really meant anything to me’, which is true. I even made my mum and a few friends get in on this experiment and we all fell into the same category. I’m not an overweight alchoholic lazy sweet-toothed tv addict who doesn’t eat fruit. HOWEVER… When I first read the options presented, I was desperately hoping there would be one to re-inforce giving up smoking, which alas there was not, so in my mind I imagined there was one, that said ‘You will not smoke your first cigarette until you leave the house’. I can proudly say that I have followed this through every day and will continue to do so, and, as a regular ‘wake-up-light-one-up’ kinda guy, I am thankful for inspiring me to do this, I often don’t have one till lunchtime now, so I thank you. Your willpower test has worked in different ways.
I’m going to mention this next bit because I have/want to. The whole wikileaks thing. OH EM GEE. I’m not going to prattle on about it or say anything, but until this month I wasn’t even aware of them, and now, during the last few weeks, and doing some serious internet searchage, I have realised that the icebergs are bigger and tippier than I could ever have imagined, and I’m not talking about anything to do with Assange, but the backlash that has followed and the current WWWW1 that is going on under our noses that no-one seems to be aware of.
It truly is history in the making, and breathtaking. Look into it people, its quite astounding.
I’m not looking forward to getting my Christmas tree because I live up a very big hill in London, and there’s no buses, and the trees are for sale at the bottom of said hill.
I gave away £2700 completely by accident earlier this year, and it wasn’t even my money to give away. It was my employers. I handed it over in cash as well. I work for a bookies. All I got was a slap on the wrist. *Don’t gamble, it’s not worth it, you will ALWAYS LOSE*
Unless your name is Brian and you came into my shop last month.
OK, I’m out of rambling power now, I could have gone on but I have to be at work in the morning *yawns*, so I bid you all a good day/night/afternoon, wherever you maybe.
P.S. The socks thing is easy, I got it in 1.5 milliseconds of my dad shagging my mum on the day I was conceived. Beat that.
December 18, 2010 at 6:00 pm
Cheer up, really
While something clearly matters to you (I find much of what you mentioned interesting), this is simply not the appropriate forum.
As for the puzzle, I had an approach straight away, a minute for the simple math and confirming the idea.
Spent 5-10 minutes trying to find more thoughtful solutions, haven’t found any though.
December 18, 2010 at 4:50 am |
Got it in 4 seconds and if I’m right, its a pretty straightforward, boring puzzle- I must be missing something.
December 18, 2010 at 4:52 am |
And his lights did not go in, his lights WENT….in his house. As in- “all my lights went (out), in my house. The ‘out’ part is understood
December 18, 2010 at 4:59 am |
Simple logic and simple math – took about 20 seconds. There is only one real answer. (But I’ve thought THAT before on these sneaky challenges!)
December 18, 2010 at 12:06 pm |
It’s all about math. 5 seconds
December 18, 2010 at 2:09 pm |
30 s. Worst case scenario approach.
December 18, 2010 at 10:51 pm |
I think I got the answer in under 30 seconds, if not almost immediately. Unless I miss my guess, the number of categories is more important than the number of socks in each.
December 18, 2010 at 11:05 pm
Whoops! I spoke too soon. I was thinking “or” logic, but the puzzle uses “and” logic.
December 19, 2010 at 11:02 am |
Less than 10 seconds. I started from thinking from the other direction of what will be left instead of what to take out.
December 19, 2010 at 11:18 am
Yes, that’s the “happy idea”
December 19, 2010 at 5:46 pm |
I’ve got an answer but I don’t get it – presumably you still can’t see the colour of the socks after pulling them out, so how do you know which two to put on your feet? If you’re going to take them outside to look at them under the street lights, you might as well take the whole drawer outside
December 19, 2010 at 7:04 pm |
I got an answer that will work fairly quickly, but I don’t like it. I’m just hoping that there’s a number smaller than mine and a way to solve it that’s far more clever.
December 19, 2010 at 7:14 pm |
Also, why are you keeping all of your socks individually in your sock drawer? Is it that hard to ball the pairs together?
December 23, 2010 at 11:36 pm |
15 sec
and I agree with Jake: ‘Also, why are you keeping all of your socks individually in your sock drawer? Is it that hard to ball the pairs together?’
December 29, 2010 at 4:57 pm |
It took me twenty seconds to come up with what is probably the wrong answer (but I secretly think it is the right answer.)