Aptitude Discussion

Q. |
A man sitting in train travelling at the rate of 50 km/hr observes that it takes 9 sec for a goods train travelling in the opposite direction to pass him. If the goods train is 187.5m long. Find its speed |

✖ A. |
40 km/hr |

✖ B. |
30 km/hr |

✖ C. |
24 km/hr |

✔ D. |
25 km/hr |

**Solution:**

Option(**D**) is correct

Let the speed of goods train be $x$ km/hr.

Then,

\((50+x)\times \dfrac{5}{18}=\dfrac{187.5}{9}\)

⇒ x= **25 km/hr**

**Edit:** For more insights into the solution check comment by **Ketaki.**

**Namrata Dash**

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Whenever we deal with such questions where there is a passenger sitting in a train and another train passes by, we dont add the length of that train to calculate the total distance in the formula i.e. Time = (length of train 1 + length of train 2)/ Relative Speed. In this case we would only take the length of 1 train (187.5m in this case) and time (9 sec) to derive at speed 25 km/hr.

Why the length of the train is not taken into consideration here?