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Another Maths conundrum
21-09-2005, 03:14 PM
Post: #1
Another Maths conundrum

This one seems so easy to me now that I know it, but I remember when I first heard of it spending ages, and then only managing it because someone told me in the end. Anyway, there are no "tricks" in the question or anything like that, or any other information you need. Assume as many matches as you need. Some people seem to get it, and others (me) just stay stuck:

Let me know how you get on.

Data:
- You have two pieces of string and some matches and nothing else.
- The pieces of string are not the same length, and the only thing you know about both pieces of string, is that if you light any end, each piece takes exactly 1 hour to burn to the other end
- the rate of burn is not steady, so it can burn slowly in some parts, fast in others, you have no idea which bits of each pice of string burn quicker or slower, you just know end to end is exactly 1 hour (ie the answer does not involve cutting in any way, as that wouldn't help anyway)

Question
- How do you accurately measure 45 minutes?
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21-09-2005, 03:24 PM
Post: #2
Another Maths conundrum
Do you light both ends of one, and one end of the other. When the first one burns out, you light the second end of the other?

That means that when the first one burns out half an hour has passed. Therefore there is half an hour burn time on the other. By lighting the other end, it reduces the time to fifteen minutes.

Plus the first thirty minutes makes forty-five?

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21-09-2005, 03:34 PM
Post: #3
Another Maths conundrum
Yup thats it fee! Still can't figure out why I couldn't do it first time, but I sure couldn't and neither could many of my co-workers.
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21-09-2005, 03:37 PM
Post: #4
Another Maths conundrum
Yay!!!

I'm hopeless with numbers, so I looked at it mainly from a problem solving stance. maybe it's something to do with left- and right-brain thinking?

I bet tonee will know :laugh:

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21-09-2005, 07:28 PM
Post: #5
Another Maths conundrum
Fee For All Wrote:Yay!!!

I'm hopeless with numbers, so I looked at it mainly from a problem solving stance. maybe it's something to do with left- and right-brain thinking?

I bet tonee will know :laugh:

If you light both ends of the first string, given that the burn rate is irregular how do you know it is exactly half an hour before it burns out?

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21-09-2005, 08:00 PM
Post: #6
Another Maths conundrum
Because I didn't think that deeply about it. Smile

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21-09-2005, 08:15 PM
Post: #7
Another Maths conundrum
The rate of burn doesn't matter Survivor, but if you light one end, you know it burns out after an hour. If you light both ends, it will burn out after 30 mins. It has to, as the flame from each end will meet when each end gets 30 mins in, wherever along the string that actually is. That you don't know where in the string the flames from both ends meet doesn't matter, all you know is that the flame from each end meets after 30 mins.
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