Multiple choice

A train moves past a telegraph post and a bridge $264$ m long in $8$ seconds and $20$ seconds respectively. What is the speed of the train in km/hr?

  1. $78.2$ km/hr
  2. $71.2$ km/hr
  3. $73.2$ km/hr

  4. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let L be length and v be speed. L/v = 8 and (L+264)/v = 20. Subtracting: 264/v = 12, so v = 22 m/s. Converting to km/hr: 22 * (18/5) = 79.2 km/hr. Since 79.2 is not listed, 'None of these' is correct.

AI explanation

Let the length of the train be L and its speed be S. Using the distance formula, L equals 8S, and L plus 264 equals 20S. Substituting the first equation into the second gives 8S plus 264 equals 20S, meaning 12S equals 264, so the speed S is 22 m/s. Converting this to km/hr by multiplying by 18/5 gives 396/5, which is 79.2 km/hr. This value is not among the listed options, so the result is None of these.

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