A motorboat can travel at 10km/hr in still water it travelled 91km/hr downstream in a river and then returned to the same place taking altogether 20hrs the rate of flow of river is
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Answer:
the rate of flow of river is 3 km/Hr
Explanation:
A motorboat can travel at 10km/hr in still water it travelled 91km/hr downstream in a river and then returned to the same place taking altogether 20hrs
Let say the rate of flow of river is F km/Hr
Motor boat speed in still water = 10 km/Hr
Distance one side = 91 km
Speed downstream = 10 + F km/Hr
Time Down stream = 91/(10 + F) hr
Speed upstream = 10 - F km/Hr
Time Upstream = 91/(10 - F) hr
Total Time = 20 Hrs
=> 91/(10 + F) + 91/(10 - F) = 20
=> 91 ( 10 - F + 10 + F) = 20 ( 10² - F²)
=> 91 * 20 = 20 ( 100 - F²)
=> 91 = 100 - F²
=> F² = 9
=> F = 3
the rate of flow of river is 3 km/Hr
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