The average speed of a train running at a speed of $30\, km / h$ during the first $100\, kilometres,$ at $40\, km / h$ during the second $100\, kilometres$ and at $50\,km / h$ during the last $100\, kilometres$ is nearly (in $km/h$)

  • A

    $38.5$

  • B

    $38.3$

  • C

    $40.0$

  • D

    $39.2$

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