Multiple choice

A train passes two persons walking in the same direction at a speed of $3$ km/hr and $5$ km/hr respectively in $10$ seconds and $11$ seconds. The speed of the train is

  1. $28$ km/hr
  2. $27$ km/hr
  3. $25$ km/hr
  4. $24$ km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let train speed be v and length be L. L = (v-3) * (5/18) * 10 and L = (v-5) * (5/18) * 11. Equating: (v-3)*10 = (v-5)*11. 10v - 30 = 11v - 55, so v = 25 km/hr.

AI explanation

Let the length of the train be L meters and its speed be S m/s. The train's relative speeds to the two walkers are S minus 3 multiplied by 5/18 and S minus 5 multiplied by 5/18. Equating the train's length based on the time taken to pass them gives L equals 10 times the first relative speed and L equals 11 times the second relative speed. Solving the equation 10 times the first speed equals 11 times the second speed gives a train speed of 25 km/hr.

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