Question
A car covers four successive 7 km distances at speeds of 10 km/hour, 20 km/hour, 30 km/ hour and 60 km/hour respectively. Its average speed over this distance is
Answer: Option C
Answer: (c)Total distance= 7 × 4 = 28 km.Total time= $(7/10 + 7/20 + 7/30 + 7/60)$ hours= $({42 + 21 + 14 + 7}/60)$ hours= $84/60$ hours = $7/5$ hoursAverage speed= $\text"Total distance"/ \text"Total time" = (28/{7/5})$ kmph= ${28 × 5}/7$ = 20 kmph
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Answer: (c)Total distance= 7 × 4 = 28 km.Total time= $(7/10 + 7/20 + 7/30 + 7/60)$ hours= $({42 + 21 + 14 + 7}/60)$ hours= $84/60$ hours = $7/5$ hoursAverage speed= $\text"Total distance"/ \text"Total time" = (28/{7/5})$ kmph= ${28 × 5}/7$ = 20 kmph
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