 Brainy Puzzles
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Join this group to post and comment. crook • Nov 5, 2006

# [Puzzle] - We have a 10 meter long queue of soldiers. The queue walked exactly 10 meters

This maybe a misfit here 😕 ! Biggie dare you touch this thread 😉

Here is the problem: We have a 10 meter long queue of soldiers. The queue walked exactly 10 meters (that means the first person walked 10 meters ahead in a straight line and others followed). As soon as the queue had started moving, the last soldier ran up to the first soldier, passed on a message to him and ran back to his position (while the queue still moving ahead). He reached his position (last in the queue) exactly at the moment the queue had traveled 10 meters.

Question: What is the distance traveled by last soldier ? aashima • Nov 5, 2006
Well the last soldier travelled 20 metres. Thats because the queue is 10 metres long. Being the last one, he would have to travel 10 metres to contact the first person and then again 10 metres back to his position. It should make any difference whether the queue is moving or still. All he needs to do is approach the first person and return back. Am I justified? Kaustubh Katdare • Nov 5, 2006
aashima
Well the last soldier travelled 20 metres. Thats because the queue is 10 metres long. Being the last one, he would have to travel 10 metres to contact the first person and then again 10 metres back to his position. It should make any difference whether the queue is moving or still. All he needs to do is approach the first person and return back. Am I justified?
Nope.

..and ran back to his position (while the queue still moving ahead).
I guess the answer has to be less than 20 meters!

-The Big K- reachrkata • Nov 5, 2006
I think the answer is 18 meters.

Am I right ???😕 Jerry • Nov 6, 2006
reachrkata
I think the answer is 18 meters.

Am I right ???😕
I know the answer but do not want to spoil the fun. 18 meters is not the correct answer.

Jerry xheavenlyx • Nov 7, 2006
NOTE: Highlight for the answer. But try solving first!

I think the answer is 30 meters!

the last guy walks the whole line and comes back too. thus w.r.t the line he has traveled 10(ffw)+10(bckward) meters andddd the total distance of the whole line had moved by 10 meters, so 10+10+10=30 meters.

😁
This can also be justified by saying that since his speed was 2x or more then others while traveling back and forth keeping in mind he took the same time to rech the end of the que. Hence the distance will be somewhat more than others within the que. HOWEVER, his displacememnt will be the same! (10m)  Kaustubh Katdare • Nov 7, 2006
xHx - you sure that's the right answer? The last person took his position as soon as the queue had travelled 10 meters. That means, to reach the first person in the queue, he must have travelled 10+x (where x<10 ) meters.

I believe the answer is close to 20 meters. I'll try to patch in the complete answer later 😁

Moreover, I guess the problem can be stated in a different way to remove the confusion. We'll have to ignore the path taken by the last person and assume that he travelled in straight line all the time.

Any thoughts?

-The Big K- xheavenlyx • Nov 7, 2006
well you are right about the 10+x part, but rememeber he even had to return! and since the whole line is 10 meters itself, he HAD to cross that much distence no matter if they were stationary or running like asses. Going and comming is 10+10.

But i maybe wrong too, really difficult imagining. Had to draw ten step images 😀

You might be confusing urself with displacement and distance maybe or mixing them up. crook • Nov 10, 2006
Of course the final answer has to be 10+2x ; 'x' being the distance first person in the queue had travelled when the last person met him. I request everyone to put a detailed explanation along with your answer so that your post makes sense 😀 . No one posted the right answer so far.

Too tough for crazy engineers :twisted: ? xheavenlyx • Nov 11, 2006
Oh my last post must have been confusing, the answer i posted was 30m not 10+10. I used that post just to explain something. Acual one is in the top. (https://www.crazyengineers.com/forum/showpost.php?p=3718&postcount=6)

Anyway, you can post the anwer😀 Getting impatient! But for now just the answer, dont explain yet.

( If we think in a simple way the distance by the first person is 5m when the messenger meets him. That gives the answer to be 10+2(5) = 20!! But I dont think thats the right answer. Aashima had given that... ) aashima • Nov 11, 2006
crook
Of course the final answer has to be 10+2x ; 'x' being the distance first person in the queue had travelled when the last person met him. I request everyone to put a detailed explanation along with your answer so that your post makes sense 😀 . No one posted the right answer so far.

Too tough for crazy engineers :twisted: ?
Yes, got the concept!!! That wasn't that tough 😔
We could decode. Anyways its always next time! Kaustubh Katdare • Nov 16, 2006

I thought CEans won't give it up unless we crack it. Crook says 30 is not the correct answer. I guess I'll have to take a pen & paper and give this problem a shot.

I will do that soon. CEans wake up!

-The Big K- Jerry • Dec 14, 2006
The_Big_K

I thought CEans won't give it up unless we crack it. Crook says 30 is not the correct answer. I guess I'll have to take a pen & paper and give this problem a shot.

I will do that soon. CEans wake up!

-The Big K-
This is no-brainer. I'm ready with the answer but I'd really want to see CEans trying out this puzzle!

Jerry
PS. I will post my answer soon. LORD_EC • Jun 28, 2007
The answer is :
10+(10*1.41) which is equal to 24.1 m..
Am I Right crook ?? Kaustubh Katdare • Jun 28, 2007
Hi Lord, how about posting the explanation? It would help others understand the solution & your approach.

-The Big K- LORD_EC • Jun 29, 2007
The explation is as follows:

The queue of soldiers and the last person moved for the identical amount of time. Hence, the ratio of the distance they covered (with their individual speed)- while person moving forward and backword - are equal.​

Let's assume that when the last person reached the first person, the queue moved X meters forward.​

[Very important line,Read it carefully]
Thus, while moving forward the last person moved (10+X) meters whereas the queue of soldiers moved X meters.

Similarly, while moving back the last person moved [10-(10-X)] X meters whereas the queue of soldiers moved (10-X) meters.

[any doubt in these 2lines then you can ask]

Therefore​

(10+X)/X = X/(10-X)
(10+X)*(10-X) = X*X​

Solving, X=7.05 meters​

Thus, total distance covered by the last person
= (10+X) + X
= 2*X + 10
= 2*(7.05) + 10
= 24.1 meters​ LORD_EC
The explation is as follows:

The queue of soldiers and the last person moved for the identical amount of time. Hence, the ratio of the distance they covered (with their individual speed)- while person moving forward and backword - are equal.​

Let's assume that when the last person reached the first person, the queue moved X meters forward.​

[Very important line,Read it carefully]
Thus, while moving forward the last person moved (10+X) meters whereas the queue of soldiers moved X meters.

Similarly, while moving back the last person moved [10-(10-X)] X meters whereas the queue of soldiers moved (10-X) meters.

[any doubt in these 2lines then you can ask]

Therefore​

(10+X)/X = X/(10-X)
(10+X)*(10-X) = X*X​

Solving, X=7.05 meters​

Thus, total distance covered by the last person
= (10+X) + X
= 2*X + 10
= 2*(7.05) + 10

= 24.1 meters​

how do we get [10-(10-x)] ? 2Novem • Dec 16, 2007
I' ve got the Ans.

it is 30 meters

want to know how?
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clue is in the first statement (We have a 10 meter long queue of soldiers)
the line has moved 10 meters.
the last soilder has moved 10 meters to reach the first soilder, since the length of the line was 10 meters.
then return 10 meters back to reach the last position.

so 10+10+10= 30 meters.

Am I Right..;-) crook • Dec 19, 2007
30m is NOT the right answer! Please try again! LORD_EC • Dec 19, 2007
@Crook
check out my answer posted some months ago.I am pretty sure that the answer that i gave is right. 😀 vishalhak • Dec 19, 2007
let me guess the answer , the correct answer is 10 meters as the initial position of first soldier is the final position of the last soldier Hi,

Tell me friends if my approach is correct or not?

• Lets the speed of last soldier as A is V1 and of first soldier as B is V2
• The only thing same in cases is Time.
• Lets the distance traveled by A to meet B is 10+X, means total distance traveled by A is 10+2X and by B is 10
• When A meet B:
• Time is same, so time = dist/speed
• (10+X)/V1 = X/V2
• (10+X)V2 = X .V1-----(i)
• When A return back to position:
• Again time is same :
• (10+2X)/V1 = 10/V2
• (10+2X)V2 = 10 .V1-----(ii)
• Dividing equation i/ii
• U will get X = sqrt of 50 ~ 7.07
• Distance Traveled by A = 10+2X = 24.1 m
~Archana crook • Dec 20, 2007
Archana & LORD_EC got the solution!

😀 Congratulations! mania45 • Feb 3, 2011
mmmmmmmmmmmmmmmmmmmm vipandeep • Feb 7, 2011
I think the question doesn't have the required information. ok let me explain

Archana's solution - she supposed that the last solider would run and meet the moving first solider and come back to the finish line. (that is 10 meters from his starting position)

Now lets just think that what if the the last solider runs fast and come back the finish line while the solider number 7 is crossing the last solider's finish line? in that case the last solider is not actually last to finish his 10 meter distance.

i would say he runs 10+x meters comes back x and (lets say y) the distance the 9th solider is from the finish line of last solider.
so that total distance traveled by last solider in this case would be

10 + x ( to meet the first)
+
x (to come back to his finish line but then he realizes he is not last so he runs back to his last position)
+
y (in back direction to his moving last position - following 9th)
+
y (again to his final finish line)

so 10+2x+2Y

now try to solve it

if have questions please raise your hand HHKPHG (Has has kar pagal ho gaya)