Great Interview Question

[gamehead200]

In this story's logic, are the following true:1. Are the treetops high? (do branches start growing near to the ground concrete?) - you could pass below2. Does the lightning strike out of the blue, or does it start raining (as it usually does)? - obvious NOP :PGL

The treetops are low enough to the ground that if you were to approach a tree that was on fire, it is likely that you would catch fire. The lightning bolt strikes a tree while its raining. If you're going on the assumption that the rain would extinguish the fire, then you're thinking of a heck of a lot of rain.

You're stranded on an island made entirely of solid concrete (comment: unlikely, but OK) in the middle of the ocean. The island has nothing but trees on it.

If these two sentences are correct then I am not human. I am an Ent and I'm not alone. We'll extinguish the flames in the water, since the sharks do not pose a threat to me and my kind.

Break off a branch to use as protection from the sharks, jump in the water to get totally wet as protection from the fire, get out of the water, run through the fire to arrive safely on the side that's already been burned.Cheers and Regards

You jump in the water and one of the sharks grabs your branch. What protection do you have from the sharks now?

Next question:

• Where would you find fresh water and food on your concrete island? You can't drink saltwater and you have no weapons to kill the sharks for food.

Perhaps it would be better to die quickly through obvious means than slowly due to thirst and starvation.

Let's not think of about long-term survival, just this one situation for now.

... but this isn't the answer. Good thinking, though)

Here we have a cognitive problem. :ph34r:An answer can be either valid or not, but NOT necessarily the one you know.The teacher in second grade asks to one pupil:

On a tree there are 13 starlings.A hunter shoots down with one shot 5 of them.How many starlings remain on the tree?

The pupil:

None, as all the others will fly away, scared by the sound of the shot.

The teacher:

That is not the right answer, but I like your way of thinking.

Then the pupil asks the (female) teacher .....jaclaz

Then I guess I didn't phrase the original question as clearly as I should have. Everything I've mentioned above and in my previous posts should clarify the situation now. If something's still unclear, feel free to ask for a clarification.

[uid0]

I'd improvise a fishing rod from a tree branch, catch me a shark, then get inside it for protection from the fire.

Given more time, sharks could be stacked up into a shark based shelter, to keep the rain off.

You wouldn't want to eat them though, shark tastes like glue.

[GrofLuigi]

Again depending on more variables: shape of the island, wind, rate at which the fire spreads, 'geometry' by which it spreads (radial/perfect circle?)...

I break one branch off, set it on fire and start another fire at the opposite end of the island (not directly oposite - imagine a triangle within a circle - touching point 1 is the thunder fire, 2 is the fire I started, and 3 is where I run to). The two fires should cancel out (burn each other's fuel).

There is a tiny flaw though - at some point I'll need to cross the 'line of fire'.

I'm dead, I know...

GL

[Guest]

[...] I am an Ent [...]

Next question:

• Where would you find fresh water and food on your concrete island? You can't drink saltwater and you have no weapons to kill the sharks for food.

Perhaps it would be better to die quickly through obvious means than slowly due to thirst and starvation.

Let's not think of about long-term survival, just this one situation for now.

I'm glad I'm an Ent. All I need is the sunlight and the abundant nutrients in the seabed. My long-term survival is covered.

[Tripredacus]

This reminds me of the olden day of playing D&D and now Gamehead is the Dungeon Master, and I'm in crazy world trying to figure out how I can get the sharks to save me from the fire.

[ricktendo]

Jump in the water, take my chance with the sharks (have dove with sharks before, there cool, only interested in fish)

[Tripredacus]

I posed this question to someone else, he said "make a boat out of the trees" and I told him he had no tools. He said "Tom Hanks didn't have tools in Cast Away". I thought Robinson Crusoe was a better idea.

[Guest]

Given the following new information I have another solution that may be more plausible:

The treetops are low enough to the ground that if you were to approach a tree that was on fire, it is likely that you would catch fire. The lightning bolt strikes a tree while its raining. [it's not raining hard enough to extinguish or prevent the spread of the fire.]

[sharks do not fear tree branches.]

Let's not think of about long-term survival

In this solution let us assume that I'm human in the real world. Further, it is known that trees cannot grow in concrete and that the trees are short as stated above. Therefore, all trees on our concrete island are potted and low enough in mass to be tipped.

The trees are dense enough to prevent a person from walking between them without coming into contact with them. However, since they're densely clustered, I will tip a nearby tree into any burning tree and cause a cascade of falling trees that will clear a path for me to an area of the island that is no longer on fire. Or, to save some trees, I simply tip trees in a line to block the spread of the fire.

I have survived the fire without tempting the sharks until my inevitable rescue by flying eagles.

Edited April 9, 2010 by 5eraph

[gamehead200]

Again depending on more variables: shape of the island, wind, rate at which the fire spreads, 'geometry' by which it spreads (radial/perfect circle?)...

I break one branch off, set it on fire and start another fire at the opposite end of the island (not directly oposite - imagine a triangle within a circle - touching point 1 is the thunder fire, 2 is the fire I started, and 3 is where I run to). The two fires should cancel out (burn each other's fuel).

There is a tiny flaw though - at some point I'll need to cross the 'line of fire'.

I'm dead, I know...

GL

Believe it or not, your answer is pretty close to the actual answer I was told. But think a bit harder... What would happen if you were to set two fires, both spreading in the same direction and burning at the same rate (ignore geometry for now)?

Given the following new information I have another solution that may be more plausible:

The treetops are low enough to the ground that if you were to approach a tree that was on fire, it is likely that you would catch fire. The lightning bolt strikes a tree while its raining. [it's not raining hard enough to extinguish or prevent the spread of the fire.]

[sharks do not fear tree branches.]

Let's not think of about long-term survival

In this solution let us assume that I'm human in the real world. Further, it is known that trees cannot grow in concrete and that the trees are short as stated above. Therefore, all trees on our concrete island are potted and low enough in mass to be tipped.

The trees are dense enough to prevent a person from walking between them without coming into contact with them. However, since they're densely clustered, I will tip a nearby tree into any burning tree and cause a cascade of falling trees that will clear a path for me to an area of the island that is no longer on fire. Or, to save some trees, I simply tip trees in a line to block the spread of the fire.

I have survived the fire without tempting the sharks until my inevitable rescue by flying eagles.

Good work at the assumptions - if I were the interviewer, I'd accept this as a valid answer.

[GrofLuigi]

Again depending on more variables: shape of the island, wind, rate at which the fire spreads, 'geometry' by which it spreads (radial/perfect circle?)...

I break one branch off, set it on fire and start another fire at the opposite end of the island (not directly oposite - imagine a triangle within a circle - touching point 1 is the thunder fire, 2 is the fire I started, and 3 is where I run to). The two fires should cancel out (burn each other's fuel).

There is a tiny flaw though - at some point I'll need to cross the 'line of fire'.

I'm dead, I know...

GL

Believe it or not, your answer is pretty close to the actual answer I was told. But think a bit harder... What would happen if you were to set two fires, both spreading in the same direction and burning at the same rate (ignore geometry for now)?

It crossed my mind (square within a circle; or other polygons). But no matter how many fires I start, I will always have to retreat to an area with trees - and I can't imagine a situation where it won't spread towards me. If I start a fire in the middle, the two fires will cancel each other out on the other side, but 'my' fire will go towards me.

It's all about geometry

GL

[Guest]

GrofLuigi is correct. Fire only ever travels in one direction: outward from the starting point. In the absence of natural restrictions in the terrain, it will spread in an expanding circular pattern. Refuge must be created before starting a new fire because fire knows no ally.

Edited April 10, 2010 by 5eraph

[submix8c]

?WTH? Am I missing something?

Standard practice is a Firebreak... Go to the middle, set another fire, follow the burn and let the original fire burn its course to previously (you) burned area. Even if it moves outward (toward you again), you can still walk around the outer unburned area back into the (your) burned area.

SOP (or is this some kind of trick question)

(edit - same answer as last two I just noticed... a little obvious)

Edited April 10, 2010 by submix8c

[gamehead200]

Again depending on more variables: shape of the island, wind, rate at which the fire spreads, 'geometry' by which it spreads (radial/perfect circle?)...

I break one branch off, set it on fire and start another fire at the opposite end of the island (not directly oposite - imagine a triangle within a circle - touching point 1 is the thunder fire, 2 is the fire I started, and 3 is where I run to). The two fires should cancel out (burn each other's fuel).

There is a tiny flaw though - at some point I'll need to cross the 'line of fire'.

I'm dead, I know...

GL

Believe it or not, your answer is pretty close to the actual answer I was told. But think a bit harder... What would happen if you were to set two fires, both spreading in the same direction and burning at the same rate (ignore geometry for now)?

It crossed my mind (square within a circle; or other polygons). But no matter how many fires I start, I will always have to retreat to an area with trees - and I can't imagine a situation where it won't spread towards me. If I start a fire in the middle, the two fires will cancel each other out on the other side, but 'my' fire will go towards me.

It's all about geometry

GL

GrofLuigi is correct. Fire only ever travels in one direction: outward from the starting point. In the absence of natural restrictions in the terrain, it will spread in an expanding circular pattern. Refuge must be created before starting a new fire because fire knows no ally.

?WTH? Am I missing something?

Standard practice is a Firebreak... Go to the middle, set another fire, follow the burn and let the original fire burn its course to previously (you) burned area. Even if it moves outward (toward you again), you can still walk around the outer unburned area back into the (your) burned area.

SOP (or is this some kind of trick question)

(edit - same answer as last two I just noticed... a little obvious)

submix8c explained it the best.

[bphlpt]

I guess that GrofLuigi and 5eraph were thinking as I was about fire traveling similar to ripples from rocks thrown in a pond - outward from the center in a circle. If that were true a firebreak wouldn't work, since as GrofLuigi stated:

"I can't imagine a situation where it won't spread towards me. If I start a fire in the middle, the two fires will cancel each other out on the other side, but 'my' fire will go towards me."

But that doesn't take into account wind, which will always drive a fire away from it faster than in can come toward it, so on the (assuming) flat concrete island it will go in mostly one direction, or at least in a spreading cone shape. And if there were absolutely no wind, it would indeed expand in a circle, but it would create wind blowing toward it from the updraft caused by the heat from the fire. You could then use that wind and create small fires at the edge of the expanding circle, where the greater heat from the larger fire would pull the other fires toward it creating a safe zone for you. Do I have the theory correct?

Cheers and Regards

[MrJinje]

You can't treat a wild-fire like a camp fire, that is rubbish, large fires radiate heat much farther than a tiny camp fire. Fact is that you would start cooking before you ever got your stick lit, so setting a fire-break will not work unless you have another way of starting it.

A wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the smoldering transition between unburned and burned material. As the front approaches, the fire heats both the surrounding air and woody material through convection and thermal radiation. First, wood is dried as water is vaporized at a temperature of 100 °C (212 °F). Next, the pyrolysis of wood at 230 °C (450 °F) releases flammable gases. Finally, wood can smolder at 380 °C (720 °F) or, when heated sufficiently, ignite at 590 °C (1,000 °F). Even before the flames of a wildfire arrive at a particular location, heat transfer from the wildfire front warms the air to 800 °C (1,470 °F), which pre-heats and dries flammable materials, causing materials to ignite faster and allowing the fire to spread faster. High-temperature and long-duration surface wildfires may encourage flashover or torching: the drying of tree canopies and their subsequent ignition from below.

Edited April 10, 2010 by MrJinje