Question : A train crosses two persons travelling at 4 km/hr and 6 km/hr in the same direction in 12 sec and 14 sec, respectively. The speed of the train is ________.
Option 1: 18 km/hr
Option 2: 26 km/hr
Option 3: 20 km/hr
Option 4: 24 km/hr
Correct Answer: 18 km/hr
Solution :
Let the speed of the train be $x$.
The relative speed of 1st person and the train is $(x-4)$ km/hr.
The relative speed of 2nd person and the train is $(x-6)$ km/hr.
According to the question,
$(x-4)×\frac{12}{3600}=(x-6)×\frac{14}{3600}$
$⇒(x-4)×6=(x-6)×7$
$\therefore x = 42-24=18$ km/hr
Hence, the correct answer is 18 km/hr.
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