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SSC Selection Post 2019 PYQ — Question 56

SSC Selection Post - Higher Secondary Level 2019 - 15 Oct 2019 • Quantitative Aptitude • Q56

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A train goes from P to Q with an average speed of u km/h and returns from Q to P with an average speed of v km/h. What is its average speed of the entire journey in km/h?

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Correct answer: A

Explanation

The correct answer is option 1 i.e.  2uvu+v{2uv \over u + v}.

Let the distance between P and Q be D km.

Time taken by train from P to Q = D/u h

Time taken by train from Q to P = D/v h

Total time = D/u + D/v

⇒ D(v + u)/uv

Now, average speed = Total distance/Total time

⇒ 2D/D[(v + u)/uv] = 2uvu+v{2uv \over u + v}