Multiple choice

A person covers half his journey by train at 60 km/hr, half the remainder by bus at 30 km/hr and the rest by cycle at 10 km/hr. Find his average speed during the entire journey. एक व्यक्ति अपनी आधी यात्रा ट्रेन से 60 किमी/घं., शेष की आधी यात्रा बस से 30 किमी/घं. और शेष साइकिल से 10 किमी/घं. की दर से तय की। तो पूरी यात्रा में उसकी औसत चाल क्या थी?

  1. 20 km/hr/किमी/घं.

  2. 12 km/hr/किमी/घं.

  3. 24 km/hr/किमी/घं.

  4. 18 km/hr/किमी/घं.
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C Correct answer
Explanation

Average speed = total distance / total time. Let total distance = 4d. Half journey (2d) by train at 60 km/h: time = 2d/60. Half of remainder (d) by bus at 30 km/h: time = d/30. Remaining (d) by cycle at 10 km/h: time = d/10. Total time = d(1/30+1/30+1/10) = d(2/30+3/30) = 5d/30 = d/6. Average speed = 4d/(d/6) = 24 km/h.

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