The fifth solution is not apt because the rate at which the strings will burn is completely random.
Anonymous
27 February 2010
I'm not surprised that some people have difficulty grasping that when you light both ends of the first string, it will take 30 minutes to burn. If the strings really do burn at a *completely random* rate, the two flames don't necessarily meet after 30 minutes. They could meet after 5 minutes or after 55 minutes!
Suppose string AB happens to have the following random burn rate. If lit at A, it takes 5 minutes to burn to C and another 55 minutes to burn to B. If lit at B, it takes 5 minutes to burn to C and another 55 minutes to burn to A. Total burn time in either direction: 1 hour. Yet if you light it at A and B simultaneously the flames will meet at C after only 5 minutes!
For this puzzle to work, you need more of a constraint on the burn rate than just "completely random".
None
4 December 2012
@ 2 strings problem: If you burn the first string at both ends and the second string at one end in the same time, after the first string burned in 30 mins you still have 30 mins left on the second string beacuse you light them up in the same time. So in order for you to add another 15 minutes you also need to light the rest of the second string at both ends.
Anonymous
4 December 2012
In the Two Strings problem, if you burn the first string at both ends and the second string at one end, you can add another 15 minutes by lighting the rest of the second string at both ends.
Anonymous
5 June 2014
The hint for the burning strings puzzle should not be 'Don't burn your candle at both ends...' as it misleads the solver. The correct approach is to burn one of the strings at both ends.
Anonymous
6 May 2016
How do you measure 45 minutes?
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Comments (6)
The fifth solution is not apt because the rate at which the strings will burn is completely random.
I'm not surprised that some people have difficulty grasping that when you light both ends of the first string, it will take 30 minutes to burn. If the strings really do burn at a *completely random* rate, the two flames don't necessarily meet after 30 minutes. They could meet after 5 minutes or after 55 minutes!
Suppose string AB happens to have the following random burn rate. If lit at A, it takes 5 minutes to burn to C and another 55 minutes to burn to B. If lit at B, it takes 5 minutes to burn to C and another 55 minutes to burn to A. Total burn time in either direction: 1 hour. Yet if you light it at A and B simultaneously the flames will meet at C after only 5 minutes!
For this puzzle to work, you need more of a constraint on the burn rate than just "completely random".
@ 2 strings problem:
If you burn the first string at both ends and the second string at one end in the same time, after the first string burned in 30 mins you still have 30 mins left on the second string beacuse you light them up in the same time.
So in order for you to add another 15 minutes you also need to light the rest of the second string at both ends.
In the Two Strings problem, if you burn the first string at both ends and the second string at one end, you can add another 15 minutes by lighting the rest of the second string at both ends.
The hint for the burning strings puzzle should not be 'Don't burn your candle at both ends...' as it misleads the solver. The correct approach is to burn one of the strings at both ends.
How do you measure 45 minutes?
Add a Comment or Suggest an Answer