A car covers four successive 8 km distances

A car covers four successive 8 km distances at speeds of 12 km/hr, 18 km/hr, 24 km/hr and 36 km/hr, respectively. Its average speed (in km/hr) over this distance is:
एक कार 8 km की चार क्रमिक दूरियाँ क्रमशः 12 km/hr, 18 km/hr, 24 km/hr और 36 km/hr की चाल से तय करती हैं। पूरी दूरी के लिए इसकी औसत चाल (km/hr में) कितनी हैं?

19.2 20 18 22.5

Detailed Solution & Logic

Correct Answer:

19.2

Each distance = 8 km
Total distance = 32 km
Total time = $ \dfrac{8}{12} + \dfrac{8}{18} + \dfrac{8}{24} + \dfrac{8}{36} $
= $ \dfrac{2}{3} + \dfrac{4}{9} + \dfrac{1}{3} + \dfrac{2}{9} $
= $ \dfrac{15}{9} = \dfrac{5}{3} $ h
Average speed = $ \dfrac{32}{5/3} $= 19.2 km/h
Answer: 19.2 km/h

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