Multiple choice

A man covers the journey from a station A to B at a uniform speed of 36 km/hr. and returnes to A with a uniform speed of 45 km/hr. His average speed for the whole journey is - एक आदमी स्टेशन A से B तक की यात्रा 36 किमी./. की एक समान चाल से तय करता है। और 45 किमी./घं. की एक समान चाल से A को वापस आता है। पूरी यात्रा में उसकी औसत चाल है-

  1. 40 km/hr./किमी./घं.

  2. 40.5 km/hr./किमी./घं.

  3. 41 km/hr/किमी./घं.

  4. 42 km/hr./किमी./घं.
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A Correct answer
Explanation

For a journey with two equal distances at speeds v1 and v2, average speed = 2v1v2/(v1+v2). Here v1 = 36 km/hr, v2 = 45 km/hr. Average speed = 2×36×45/(36+45) = 3240/81 = 40 km/hr. This formula accounts for the time-weighted average - more time is spent at the slower speed.

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