I'm SMRT!!! Apparently now the riddle thread | Forums

[rlmergeuser]

It still makes no sense

[rlmergeuser]

You have two ropes and a lighter. Both ropes are exactly the same. Both ropes share the same property that, when lit at one end, the rope will burn for exactly 60 minutes. The ropes, however, do not necessarily burn at a constant rate, meaning it may take 59 minutes for one half of the rope to burn, and one minute for the final half (or any other combination of burn rates, it's random).

Using these two ropes and a lighter, how could you time exactly 45 minutes?

Smart Girl Starfire knows te answer!

Rope 1: Light both ends simultaneously and when the fire intersects you will know exactly 30 minutes have passed.
Rope 2: Light the fire from one end and the exact point of intersection for the fire seen in rope 1 simultaneously. When the fire intersects you will know exactly 15 minutes have passed.

Never mess with a girl!

[rlmergeuser]

You have two ropes and a lighter. Both ropes are exactly the same. Both ropes share the same property that, when lit at one end, the rope will burn for exactly 60 minutes. The ropes, however, do not necessarily burn at a constant rate, meaning it may take 59 minutes for one half of the rope to burn, and one minute for the final half (or any other combination of burn rates, it's random).

Using these two ropes and a lighter, how could you time exactly 45 minutes?

Smart Girl Starfire knows te answer!

Rope 1: Light both ends simultaneously and when the fire intersects you will know exactly 30 minutes have passed.
Rope 2: Light the fire from one end and the exact point of intersection for the fire seen in rope 1 simultaneously. When the fire intersects you will know exactly 15 minutes have passed.

Never mess with a girl!

Very close, but...no. Remember, the two ropes have random burn rates, so your solution wouldn't necessarily time out to exactly 45 minutes. I do appreciate the effort, though. I like you, Starfire.

[willyums]

i think theres a flaw in this one somewhere. if the burn rates are random, theres no constant to get any fixed time from

[rlmergeuser]

I googled the answer and star sounds like he/she might have it. Maybe if star explained it better?

[rlmergeuser]

Draw some diagrams, say 20 min burn time for the left half of the rope, and 40 min burn time for the right half of the rope. You'll see that the fires on rope 1 will intersects in 30 min guaranteed. And since rope 2 is exactly the same as rope 1, the fires on rope 2 intersect in 15 minutes (same logic as for rope 1). The fires are guaranteed to intersect in 30 minutes, where they intersect depends on how they burn on the rope, which is unknown, so we don't know where they will intersect.

Edited: Didn't catch your response. You said the ropes are the same. Therefore they cannot burn randomly.

[willyums]

assuming they do meet in the middle at 30mins even though the burn rate is said to be completely random, and assuming starfires only slightly wrong;

light both ends of rope 1 and one end of rope2.
when rope1 burns out at the middle (30mins), light the other end of rope2 (which has already burnt for 30mins) and the closing gap until rope2 burns out would be 15mins.

[rlmergeuser]

assuming they do meet in the middle at 30mins even though the burn rate is said to be completely random, and assuming starfires only slightly wrong;

light both ends of rope 1 and one end of rope2.
when rope1 burns out at the middle (30mins), light the other end of rope2 (which has already burnt for 30mins) and the closing gap until rope2 burns out would be 15mins.

THat makes sense, mister. I think we can put that one to rest

[rlmergeuser]

That has the exact same logic as what I said. The only difference is Willy burns up the entire rope 2 while I said start off from the point of intersection for rope 1.

[rlmergeuser]

Well your answer hurt my brain. His didn't. I suppose we have TWO winners, and can double restify this here riddle. But no one's figured mine out yet