Posted on 05/15/2025 9:41:05 PM PDT by Red Badger
This simple puzzle recently appeared in a members-only newsletter. Think you can crack it?
You have two ropes coated in oil to help them burn. Each rope will take exactly one hour to burn all the way through. However, the ropes don’t burn at constant rates; there are spots where they burn a bit faster and spots where they burn a bit slower, but it always takes one hour to finish the job. With a lighter to ignite the ropes, how can you measure exactly 45 minutes?
Fold them in half... fold them a second time. Tie them together where a matching end fold was. Light the longer free ends of both. When the burns hits the knot... 45 minutes.
“Burn one rope at both ends, and light the second rope at one end. The first rope will burn through in a half hour and the second rope will burn halfway through.”
Rope 1 — Yes, regardless of local burn rates, the rope will burn through in 30 minutes.
Rope 2 — No. The second rope could burn through 90% in that 30 minutes. Or it could burn through 10% in that 30 minutes. So you have no way of knowing if Rope #2 will burn halfway through.
You wrote “it’s explained in 7”
How do you figure that?
“Burn one rope at both ends, and light the second rope at one end. The first rope will burn through in a half hour and the second rope will burn halfway through.”
Rope 1 — Yes, regardless of local burn rates, the rope will burn through in 30 minutes.
Rope 2 — No. The second rope could burn through 90% in that 30 minutes. Or it could burn through 10% in that 30 minutes. So you have no way of knowing how long it will take Rope #2 to burn halfway through.
It’s not length that matters, it’s time. No matter which end you start, it takes 1 hour to burn. If you start at both ends it takes half the time. So if one rope has burned for 30 minutes, there is only 30 minutes left. With both ends burning, only 15 minutes left. This is basic algebra guys.
“Can the ropes transition to steel cable? ”
Anyone against this transition is a hater.
A anti trans steel hater.
7 is not an answer because it violates the problem.
Please don’t be ignorant. And if you are going to be ignorant, don’t infect others.
Then you’ll need to stay off the Internet.
No, you cannot say half the rope burns in half the time since the problem says the burn rate is not linear.
FIFY
The only main difference is that you stated “the second rope will burn halfway through.” That left it unclear whether you meant halfway through by length or by time. Of course, you meant by time.
That’s what she said.
Oh... That’s not the burning rope trick that I know... And you don’t want to.
He means halfway through by time! Leaving 30 minutes total for whatever length is left. Burning that remainder from both ends leaves 15 minutes total time.
Does England have a 4th of July?
If you’re going down a river in a wire canoe, and one of your wheels falls off, how many pancakes does it take to cover a doghouse?
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