Asadullah Ansari

Build-Up Your Problem Solving Skill : Specially Using By C/C++/Data Structure Puzzles/New Technique Algorithm Design/ Understanding New Technology

solve this puzzle?

Posted by asadullahansari on August 20, 2008

Two boys walking in the woods decide to take a shortcut thru a railroad tunel. When they had walked 2/3 of the way, their worst fears were realized. A train was coming in the opposite direction, nearing the tunnel entrance. They boys panicked and each ran for a different end of the tunnel. Both boys ran at the same speed, 10 miles per hour Each boy escaped from the tunnel just at the instant the train would have squashed him. Assuming the train’s speed was constant, and both boys were capable of instantaneous reaction and acceleration, how fast was the train going?

4 Responses to “solve this puzzle?”

  1. Sriram said

    15 miles/hour.

  2. Excellent !!! Thanks for solving… More welcome to answer this puzzle.

  3. But I think 30 miles/hour

  4. Boy1 and Boy2 are two boys ..Lets assume!!!
    Boy1 is running apposite away from train
    Boy2 is running in the direction of train
    Length of tunnel L
    speed of train V

    since 2/3 roads down the tunnel already.

    Boy2 covers 1/3 L at a speed of 10 miles/hr

    Boy1 covered 1/3 L in the opposite direction

    Time taken by Boy1= (1/3L)/10 = L/30

    time= L/V

    L/30 = L/V

    V=30 mph

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