One fourth of a journey is covered at the rate of 50 km/h, one third at the rate of 60 km/h and the rest at the rate of 100km/h. Find the average speed for the whole journey.
Correct Answer: Option C
Let, the total distance travelled by train be ‘x’ km.
⇒ Time taken to travel one fourth part \(= \frac{{\frac{x}{4}}}{{50}} = \frac{x}{{200}}\)
⇒ Time taken to travel one third part \(= \frac{{x/3}}{{60}} = \frac{x}{{180}}\)
⇒ Time taken to travel rest part (5/12) \(= \frac{{\frac{{5x}}{{12}}}}{{100}} = \frac{x}{{240}}\)
∴ Total time taken in the journey = \(\frac{{53\;x\;}}{{3600}}\)
Average speed of the whole journey = total distance/total time
\(= \frac{x}{{\frac{{53x}}{{3600}}}}\; = \frac{{3600}}{{53}}\;\;{\rm{km}}/{\rm{h}}\)
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