top button
Flag Notify
    Connect to us
      Site Registration

Site Registration

How fast did the courier bike, when he delivers a letter on moving column?

+3 votes

A military column of 1 km length marches with a constant speed of 6 kilometers per hour. A courier from the back of the column is sent to the head of the column by bike to deliver a message. Arrived at the front, he instantly returns. When he returns at the back, the column has traveled a distance of 1 km since the start of his errand. The courier drove with constant speed.

posted Feb 12, 2014 by Bhani Bhosle

Share this puzzle
Facebook Share Button Twitter Share Button LinkedIn Share Button

2 Answers

+1 vote

The relative speed of the courier (compared to the column) is v-6 on the journey to the front, and v+6 on the way back. The distance traveled (relatively to the column) by the courier is in both cases 1 km, therefore the total time he is biking is

1       +      1   
v - 6        v + 6

The column travels 1 km in 10 minutes (1/6 hour), therefore

   1    +      1    = 1/6
  v - 6      v + 6

This can be written as a quadratic equation (v+6) + (v-6) = (v-6) × (v+6) / 6 with as only allowed solution v = 6 + 6 × sqrt(2) km/h (approximately 14.49 km/h).

answer Feb 12, 2014 by Bhani Bhosle
0 votes

Dear ans is 12 km/hr.............too easy

answer Oct 20, 2015 by Vikrant Mane

Similar Puzzles
+1 vote

Aaditya was gifted a new bike. He drove x km at 55 kmph.
Then he drove x+20 km at 40 kmph.
He drove his bike for 100 minutes.
How much distance did he travel?

+1 vote

Today is very icy and cold morning in the Newcastle.

Mr. Shearer, an office bus driver arrived to pick the employees from the last stop. Shearer suddenly remembers that he needs to pick a newly joined 4miles to the north. Mr. Shearer lost his direction compass, a few minutes later Shearer is able to figure that he is moving in the correct direction i.e. north.

How did Shearer know that he is moving in the correct direction?

0 votes

Rohan buys an old bike for Rs. 13500 and spends Rs. 4250 on its repairs.
If he sells the bike for Rs. 27000, what is his gain in percent?

0 votes

Jatin was trying to take a short cut through a very narrow tunnel when he heard the whistle of an approaching train behind him.
Having reached three-eights of the length of the tunnel, he could have turned back and cleared the entrance of the tunnel running at 10 km per hour just as the train entered.
Alternatively, if he kept running forward, the train would reach him the moment he would jump clear of the tracks.
At what speed was the train moving?