Question
A motorboat in still water travels at a speed of 40 km/hr. It goes 45 km upstream in 2 hour 15 minutes. The time taken by it to cover the same distance down the stream will be :
Solution
Speed of the motorboat upstream = 45/(9/4) = 20 km/hr Let the speed of the current be x km/hr ⇒ 40 – x = 20 ⇒ x = 20 km/hr Speed of motor boat downstream = 40 + 20 = 60 km/hr Time taken to cover 45 km at 60 km/hr = 45/60 = 3/4 hours or 45 minutes
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