What's the quickest way to solve this teamwork puzzle?
June 17, 2010 7:42 AM Subscribe
During the assessment training programme for the Army, there's one specific puzzle that keeps tripping me up; and I have to be prepared for. Any ideas?
I think I've got good solutions for the others, but this one's eluding me. I've searched all over, but I can't seem to find solutions on the Net. It goes as follows:
Under the assumption that your team is supplying forward infantry, you have to cross a "minefield". This consists of five stepping stones, arranged similarly to the number 5 on a die.
You are given two planks (one long, one short), a tyre, and a jerry can (the "supplies"). You must get all eight members of your team, plus the jerry can, to the other side, as fast as possible.
Limitations: No person or the "supplies" may touch the ground- only the tyre can. The planks can be laid across the tyre. No more than two people may occupy a stepping stone at any one time. The short plank is long enough to reach between the two stones at the beginning and end, but only the long plank reaches between the start/end and the centre.
I can work out solutions readily enough, but I'm convinced there's a simple, elegant answer that I'm completely missing. Any geometrists or logicians around? If I've left out any info by accident, feel free to ask.
I think I've got good solutions for the others, but this one's eluding me. I've searched all over, but I can't seem to find solutions on the Net. It goes as follows:
Under the assumption that your team is supplying forward infantry, you have to cross a "minefield". This consists of five stepping stones, arranged similarly to the number 5 on a die.
You are given two planks (one long, one short), a tyre, and a jerry can (the "supplies"). You must get all eight members of your team, plus the jerry can, to the other side, as fast as possible.
Limitations: No person or the "supplies" may touch the ground- only the tyre can. The planks can be laid across the tyre. No more than two people may occupy a stepping stone at any one time. The short plank is long enough to reach between the two stones at the beginning and end, but only the long plank reaches between the start/end and the centre.
I can work out solutions readily enough, but I'm convinced there's a simple, elegant answer that I'm completely missing. Any geometrists or logicians around? If I've left out any info by accident, feel free to ask.
Best answer: Assuming the stones are laid out like:
- Short plank between 1 & 2.
- Long plank between center of short plank and 3.
- Two people walk along long plank to 3.
- Toss/place tire midway between 4 and 5.
At this point it looks like this:
- Guy left in the center (3) rotates long plank back and forth until everyone has crossed.
That's about as simple as it gets, I think.
posted by EndsOfInvention at 7:56 AM on June 17, 2010
FINISH 4 5 3 1 2 STARTHow about:
- Short plank between 1 & 2.
- Long plank between center of short plank and 3.
- Two people walk along long plank to 3.
- Toss/place tire midway between 4 and 5.
At this point it looks like this:
4 O 5 3 | | 1--|---2- Move long plank to between 3 and the tire:
4 O 5
|
|
3
1-----2
- One person moves across from 3 to finish. - Guy left in the center (3) rotates long plank back and forth until everyone has crossed.
That's about as simple as it gets, I think.
posted by EndsOfInvention at 7:56 AM on June 17, 2010
I'm assuming it's an elongated X, otherwise the distance from "start/end" to the center would be shorter than between the two start or end stones:
If so (X=stone, o=tire, line=plank):
posted by whatnotever at 7:56 AM on June 17, 2010
If so (X=stone, o=tire, line=plank):
X X o-X | | X XStand everyone on the middle stone and the short plank. Swap the long plank over:
X X | | o-X X XIf not everyone can fit on the short board, flip the long one back and forth as many times as needed to get everyone across.
posted by whatnotever at 7:56 AM on June 17, 2010
If you're allowed to stand a bunch (>2) of people on the short plank (avoiding the 2 per stepping stone rule), then whatnotever's solution is better.
posted by EndsOfInvention at 7:58 AM on June 17, 2010
posted by EndsOfInvention at 7:58 AM on June 17, 2010
Response by poster: Excuse the horrific scrawls, but here's a brief outline. Sort of.
posted by malusmoriendumest at 8:01 AM on June 17, 2010
posted by malusmoriendumest at 8:01 AM on June 17, 2010
Response by poster: And no more than two people on a plank, no more than two people on a stone (even in passing), and no throwing anything. I think that's what the NCO said.
posted by malusmoriendumest at 8:02 AM on June 17, 2010
posted by malusmoriendumest at 8:02 AM on June 17, 2010
Response by poster: Liking the T-shape, though- my previous solutions were foolishly complicated combinations of diagonal links :D
posted by malusmoriendumest at 8:03 AM on June 17, 2010
posted by malusmoriendumest at 8:03 AM on June 17, 2010
Haven't come across this one, but if it helps in your googling, the British Army calls these 'leaderless tasks' or 'command tasks'. I've done similar ones, but not this precise one, which seems more like a logic puzzle.
posted by Happy Dave at 8:06 AM on June 17, 2010
posted by Happy Dave at 8:06 AM on June 17, 2010
Response by poster: Found a video scenario online, cheers to Happy Dave. Should help visualising EndsOfInvention/whatnotever's solutions a bit more clearly
posted by malusmoriendumest at 8:09 AM on June 17, 2010
posted by malusmoriendumest at 8:09 AM on June 17, 2010
no throwing anything
To place the tire in my solution you can still place it on the ground and push into place with the long plank, if allowed.
posted by EndsOfInvention at 8:10 AM on June 17, 2010
To place the tire in my solution you can still place it on the ground and push into place with the long plank, if allowed.
posted by EndsOfInvention at 8:10 AM on June 17, 2010
Response by poster: Yeah, that's allowed and works fine. I think I've got it now, thanks all ^.^
posted by malusmoriendumest at 8:12 AM on June 17, 2010
posted by malusmoriendumest at 8:12 AM on June 17, 2010
Wait, can the long plank make the diagonal from 1-3? If so, why isn't the solution just to place the long plank on 1-3, have two people walk out, have one of them rotate it around to 3-4 and let the other guy walk to the finish, and repeat as necessary for everyone with the "bridge man" staying on three and rotating the plank as necessary (and some people carrying supplies as necessary). When the last guy is over, the bridge man crosses and we're done? Why do you need the t[i|y]re and the short plank?
posted by The Bellman at 8:18 AM on June 17, 2010
posted by The Bellman at 8:18 AM on June 17, 2010
Best answer: This is going to sound obvious, but don't allow any of your team to "roll" the tyre - it will inevitably roll outside of your reach, leaving you stranded and looking silly.
posted by Simon_ at 8:19 AM on June 17, 2010
posted by Simon_ at 8:19 AM on June 17, 2010
Response by poster: Mostly for reasons of stability- with a time limit you can't take your time placing the planks. And if one person slips or knocks the plank and it touches the ground, we all lose.
posted by malusmoriendumest at 8:20 AM on June 17, 2010
posted by malusmoriendumest at 8:20 AM on June 17, 2010
Best answer: Bellman: If the long plank is exactly the right size to reach from the end to the center, and no longer, it will not reach the diagonal.
posted by EndsOfInvention at 8:20 AM on June 17, 2010
posted by EndsOfInvention at 8:20 AM on June 17, 2010
Can the men simply step up onto one of the stones at the start (and off again at the finish) or are planks necessary for this bit too?
If they CAN just step onto the start then the short plank is not necessary.
1) Lay the long plank between a stone at the start and the centre.
2) Have two men walk to the centre along this plank, one carrying the jerry can.
3) Now, one of these two men can lift the long plank and place it between the centre and a stone on the other side.
4) The man with jerry can walks to the other side (the finish), while the other remains in the centre.
5) The man in the centre then lifts the long plank and returns it to the original position to allow another man to come to the middle (perhaps carrying the tyre).
6) Again, the long plank can be lifted and turned to reach the finish, allowing one of the people in the centre to reach the far side.
8) Repeat.
posted by jonesor at 8:25 AM on June 17, 2010
If they CAN just step onto the start then the short plank is not necessary.
1) Lay the long plank between a stone at the start and the centre.
2) Have two men walk to the centre along this plank, one carrying the jerry can.
3) Now, one of these two men can lift the long plank and place it between the centre and a stone on the other side.
4) The man with jerry can walks to the other side (the finish), while the other remains in the centre.
5) The man in the centre then lifts the long plank and returns it to the original position to allow another man to come to the middle (perhaps carrying the tyre).
6) Again, the long plank can be lifted and turned to reach the finish, allowing one of the people in the centre to reach the far side.
8) Repeat.
posted by jonesor at 8:25 AM on June 17, 2010
jonesor: that's my solution as well, but apparently the long plank isn't quite long enough to make the diagonal.
posted by The Bellman at 9:13 AM on June 17, 2010
posted by The Bellman at 9:13 AM on June 17, 2010
In general I've found that in many of the "two plank" puzzles that using one plank as a support for the other is usually the cognitive leap that most people miss.
posted by bitdamaged at 9:27 AM on June 17, 2010
posted by bitdamaged at 9:27 AM on June 17, 2010
I apologize for a potentially silly question - and why I would fail miserably at this kind of test :) but...
Why can the tire touch the ground? Any way of placing the tire would seem to have the potential to detonate a mine.
posted by NoDef at 10:27 AM on June 17, 2010
Why can the tire touch the ground? Any way of placing the tire would seem to have the potential to detonate a mine.
posted by NoDef at 10:27 AM on June 17, 2010
From the description in the video it seems to me that you cannot reach the first stones without the short plank to help you and you can't abandon any of your equipment. The tire is actually not that useful because you have to have it with you in the end. Furthermore there are obviously great bit of difficulty in doing almost any of the tasks, including setting up the planks and crossing them so such operations should obviously be kept to a minimum. Both the crossing and setting up of planks is easier with a person helping on the receiving end. The bottleneck is obviously the middle island. Any plan is going to have a single person there, moving the long plank.
My plan: Use short plank to quickly move two people each on platforms 1 and 2. Leave the short plank between the beginning and 2. Then use long plank to push the tire right next to 3. Place the long plank between 2 and 3 (using the tire to help keep it stable if possible, if not the tire can be ignored and treated as an extra jerry can) move two people from 2 to 3. They will then place the plank between 3 and 4, again using the tire for balance as needed, either by pushing it or leaving it near platform 3 to help with stability.
The long plank will then be used to ferry two people each to platforms 4 and 5. (This will require an extra move across a plank not held by someone at the other end so is a bit risky.) The last person to leave 2 brings the short plank. At this point we have 2 people on each platform except 2. The short plank is placed between 5 and finish. The 2 people on 1 are also ferried over. 1 and 5 are emptied, the people in finish place the short plank between finish and 4 and the long plank is placed between 3 and 4. Move everyone to the end, take your stuff with me and you are done.
posted by Authorized User at 10:27 AM on June 17, 2010
My plan: Use short plank to quickly move two people each on platforms 1 and 2. Leave the short plank between the beginning and 2. Then use long plank to push the tire right next to 3. Place the long plank between 2 and 3 (using the tire to help keep it stable if possible, if not the tire can be ignored and treated as an extra jerry can) move two people from 2 to 3. They will then place the plank between 3 and 4, again using the tire for balance as needed, either by pushing it or leaving it near platform 3 to help with stability.
The long plank will then be used to ferry two people each to platforms 4 and 5. (This will require an extra move across a plank not held by someone at the other end so is a bit risky.) The last person to leave 2 brings the short plank. At this point we have 2 people on each platform except 2. The short plank is placed between 5 and finish. The 2 people on 1 are also ferried over. 1 and 5 are emptied, the people in finish place the short plank between finish and 4 and the long plank is placed between 3 and 4. Move everyone to the end, take your stuff with me and you are done.
posted by Authorized User at 10:27 AM on June 17, 2010
I am guessing that one of the constraints is that nothing can be left behind. So I think Authorized User has the solution.
But, if you are looking for something simpler... Can the tire support both planks at once? And is it OK to leave the tire behind?
If so, you could use the short plank to get to platform 1, use the long plank to push the tire along the ground (don't roll it) toward platform 4, then balance the long plank across platform 1 and the tire. Walk out to the end of the long plank (above the tire), put the short plank across the tire and platform 4. Then position one person on platform 4 and one person on platform 1, to rotate the planks alternately toward the tire and toward safe ground at either end of the course. The others go one at a time across the short plank to platform 1, across the short plank to the tire, across the long plank to platform 4, across the long plank to the end.
Does that make sense? This way you could take both planks with you, but the tire would be left behind.
posted by beandip at 9:20 PM on June 17, 2010
But, if you are looking for something simpler... Can the tire support both planks at once? And is it OK to leave the tire behind?
If so, you could use the short plank to get to platform 1, use the long plank to push the tire along the ground (don't roll it) toward platform 4, then balance the long plank across platform 1 and the tire. Walk out to the end of the long plank (above the tire), put the short plank across the tire and platform 4. Then position one person on platform 4 and one person on platform 1, to rotate the planks alternately toward the tire and toward safe ground at either end of the course. The others go one at a time across the short plank to platform 1, across the short plank to the tire, across the long plank to platform 4, across the long plank to the end.
Does that make sense? This way you could take both planks with you, but the tire would be left behind.
posted by beandip at 9:20 PM on June 17, 2010
They do this in civilian team building. The answer is always to make a T. 'Normal' thinking is to try to move from one area to the next using a single plank, followed by frustrated attempts to throw stuff, jump, or magically join the planks together. The islands are positioned to be initially within reach, then suddenly out of reach once you're out there. Apparently, magical unicorn synergistic power-team thinking is the T.
posted by obiwanwasabi at 2:26 AM on June 18, 2010
posted by obiwanwasabi at 2:26 AM on June 18, 2010
Well the gap needs to be crossable with just a single plank, otherwise the task is impossible without leaving a team member or a plank behind. Surely you can use the T-method to make it more stable for the first 6 (or 7 if you ferry the short plank) to cross but it needs to be crossed using the long plank alone, at least once.
posted by Authorized User at 9:47 PM on June 18, 2010
posted by Authorized User at 9:47 PM on June 18, 2010
This thread is closed to new comments.
Can you catapult things across?
posted by stereo at 7:49 AM on June 17, 2010