Chinahand Posted April 16, 2015 Share Posted April 16, 2015 That's like the one where you are given the following instructions: Start a stop watch. Go and switch you bedroom light on for one hour. Then go and switch it off for half an hour. Then go and switch it on for fifteen minutes Then go and switch it off for 7 and a half minutes. Keep doing the same routine. Is your bedroom light switch on or off after 2 and a half hours? Quote Link to comment Share on other sites More sharing options...
wrighty Posted April 16, 2015 Share Posted April 16, 2015 Impossible to say on those instructions China - the series converges on 2 hours. I suspect the switch will however be neither on nor off but broken. Unless of course you mean to repeat those 4 instructions rather than follow the ever decreasing pattern, in which case after 2 and a half hours it'll be on. Quote Link to comment Share on other sites More sharing options...
thebees Posted April 16, 2015 Share Posted April 16, 2015 Whatever, yer mother will go mad, don't you know "It costs10p every time you switch that light on and off"? 2 Quote Link to comment Share on other sites More sharing options...
Albert Tatlock Posted April 16, 2015 Share Posted April 16, 2015 Mine was off after two and a half hours. All that cocking about blew the bulb. Quote Link to comment Share on other sites More sharing options...
Monkey boy Posted April 16, 2015 Share Posted April 16, 2015 (edited) June 17th. July 16th? Edited April 16, 2015 by Monkey boy Quote Link to comment Share on other sites More sharing options...
Chinahand Posted April 17, 2015 Share Posted April 17, 2015 Oh what the heck one last maths question on a Friday Night! You are planning to drive across the Golden Gate Bridge turn round and come back - 3 miles from start to finish. And being a bit of a neurotic you want to do it at exactly the speed limit 55mph. Sadly you get held up and after a mile you've only averaged 18.3333 mph. On average how fast must you drive the remaining 2 miles to achieve your wish? 1 Quote Link to comment Share on other sites More sharing options...
wrighty Posted April 17, 2015 Share Posted April 17, 2015 c 1 Quote Link to comment Share on other sites More sharing options...
The Old Git Posted April 20, 2015 Share Posted April 20, 2015 Sounds like you'd enjoy http://www.futilitycloset.com/ Quote Link to comment Share on other sites More sharing options...
dilligaf Posted April 20, 2015 Share Posted April 20, 2015 Quite simply, NO 1 Quote Link to comment Share on other sites More sharing options...
Monkey boy Posted April 22, 2015 Share Posted April 22, 2015 Oh what the heck one last maths question on a Friday Night! You are planning to drive across the Golden Gate Bridge turn round and come back - 3 miles from start to finish. And being a bit of a neurotic you want to do it at exactly the speed limit 55mph. Sadly you get held up and after a mile you've only averaged 18.3333 mph. On average how fast must you drive the remaining 2 miles to achieve your wish? To travel 3 miles at 55mph (miles / hour) would take you; 55 = 3/h so 55h = 3 so 3/55= h = 0.05454 hours. Travelling 1 mile at 18.333 mph would take you 18.3 = 1/h so 1/18.333 = h = 0.05454 hours So Wrighty is right. 1 Quote Link to comment Share on other sites More sharing options...
Chinahand Posted April 22, 2015 Share Posted April 22, 2015 Yep, it's a trick question. Usually if you try to solve it using standard maths techniques for average speeds you end up trying to divide by zero. The point of the question is to get you to think why it is making you divide by zero - you haven't made a mistake, the question is requiring you to instantaneously get to the finish point - something that requires either infinite speed or stopping time - hence c is the right answer! Your explanation gets that point perfectly. 1 Quote Link to comment Share on other sites More sharing options...
wrighty Posted April 22, 2015 Share Posted April 22, 2015 When averaging speeds you have to use the harmonic mean. For example travel a mile at 60mph and then a mile at 30mph - what's your average speed? Not 45mph, which is the obvious answer, but 1/(0.5x(1/60 + 1/30)) - average the reciprocals and then reciprocate. 1 mile at 60mph takes 1 minute, 1 mile at 30mph takes 2 minutes, so the average speed is 2 miles in 3 minutes, or 40mph. This question is basically this - what speed do you have to travel to solve 55=1/(1/3x(2/? + 1/18.3333)) (it's a weighted harmonic mean) and the ? comes out as infinite. Speed of light is as close as you can get, and taking into account special relativity, it is basically infinite - but that's for another thread. 2 Quote Link to comment Share on other sites More sharing options...
Chinahand Posted June 5, 2015 Share Posted June 5, 2015 Another Math's question confusing the heck out of GCSE students: 'There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow. 'Hannah takes a sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet. 'The probability that Hannah eats two orange sweets is 1/3. Show that n²-n-90=0' Link Quote Link to comment Share on other sites More sharing options...
wrighty Posted June 5, 2015 Share Posted June 5, 2015 Too easy! The comments on that link are laughable - 4 accountants taking 2 hours to solve it. Don't think they'll be doing my tax return. I'll try my kids with it later - one's just done GCSE but a different exam board, the other got an A* GCSE last year and has just done AS. I'll be disappointed if it takes them much longer than the few moments it took me to solve. Quote Link to comment Share on other sites More sharing options...
Tarne Posted June 5, 2015 Share Posted June 5, 2015 Another Math's question confusing the heck out of GCSE students: 'There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow. 'Hannah takes a sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet. 'The probability that Hannah eats two orange sweets is 1/3. Show that n²-n-90=0' Link Yeah, that's a piece of piss, and I think the problems just come from not reading the question properly. Hanna getting 2 orange sweets is 1/3, so 1/3 = 6 out of n chance it'll be orange * 5 out of n - 1 chance it'll be orange 1/3 = 6/n * 5/n-1 Re-arrange it 1/3 = (6*5) / n(n - 1) 1/3 = 30 / n squared - n 1 = 90 / n squared - n 90 = n squared - n 0 = n squared - n - 90 Quote Link to comment Share on other sites More sharing options...
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