Burning ropes to measure time

Agent Smith

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Oct 18, 2023
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462
A question from another forum. Would like some clarification, tips and hints.

Two ropes, A and B. A burns in 50 minutes and B burns in 41 minutes (they burn at a uniform rate). Can we use the 2 ropes to measure 33 minutes?

I came up with an equation: 50x+41y=33z50x + 41y = 33z. We would like for z=1z = 1

The answer (what I think is the answer anyway): 502=25\frac{50}{2} = 25 and 25+41=6625 + 41 = 66 and 662=33\frac{66}{2} = 33

For my equation: x=14x = \frac{1}{4} and y=12y = \frac{1}{2} and z=1z = 1

50×14+41×12=33×1=3350 \times \frac{1}{4} + 41 \times \frac{1}{2} = 33 \times 1 = 33

Correct?

We should've been given 22 sets of equations as there are 22 variables.

Comments/criticisms/etc.
 
Does your solution x=1/4 and y=1/2 mean that we measure 1/4 of rope A and half of B and burn these portions glued together or first burn rope A and then immediately burn the B portion?

I tried burning A at both ends and one end of B simultaneously. Then when A has burned up we have 16 minutes remaining of rope B. Now I burned the other end of rope B, which cuts the remaining time down to 8 min. Then the total time is 25 min + 8 min = 33 min.
 
@Aion gracias for the correct solution.

Si, my "solution" involves cutting rope A into fourths and rope B into half. It's clumsy compared to your slick solution.

The only "advantage" I have is I have left over 3 segments, each 12.5 minutes long and 1 segment 20.5 minutes long.

Gracias.
 
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