# SPEED question Classic List Threaded 7 messages Open this post in threaded view
|

## SPEED question

 Relations between South and North Korea have been tense lately. In this backdrop, a North Korean troop 5 meters long starts marching. A soldier at the end of the file steps out and starts marching forward at a higher speed. On reaching the head of the column, he immediately turns around and marches back at the same speed. As soon as he reaches the end of the file, the troop marching and it is found that the troop has moved exactly 5 metres. Which of the following could be the distance travelled by the soldier? This question is from here and the link also possesses answer, which I can't understand. how did we get to know (5/x+y) + (5/x–y) = 5/y etc.? after calculation how we got x/y = (1 +- 2^1/2)/1? If anyone knows these answers please share. Thanks.
Open this post in threaded view
|

## Re: SPEED question

Open this post in threaded view
|

## Re: SPEED question

Open this post in threaded view
|

## Re: SPEED question

 Thank you sir. How did you derive x/y ? I am stuck here: see this  and I can't get  x/y = (1 +- 2^1/2)/1. Where am I wrong?
Open this post in threaded view
|

## Re: SPEED question

 Hi XIPP,My name is Aditya! (Well i prefer Adi :) )For our earlier eqn:5/(x-y)+ 5/(x+y)=5/y. Take 5/x common from both sides, and we have 1/(1 - y/x) + 1/(1 + y/x) = 1/(y/x) Take y/x = z.(for simplification purpose only) => 1/(1-z) + 1/(1+z) = 1/z    => 2/(1-z^2)=1/zor z^2 -2z -1 = 0 On solving z, z = (2 +-8^(1/2))/2 = (1+-2^1/2)/1 =x/y And that's last missing piece of our puzzle! On Sun, Dec 1, 2013 at 10:57 AM, XIPP [via Discussion forum] wrote: Thank you sir. How did you derive x/y ? I am stuck here: see this  and I can't get  x/y = (1 +- 2^1/2)/1. Where am I wrong? If you reply to this email, your message will be added to the discussion below: http://discussion-forum.2150183.n2.nabble.com/SPEED-question-tp7584279p7584285.html To start a new topic under General Discussions, email [hidden email] To unsubscribe from General Discussions, click here. NAML "Woh mara papad wale ko!"