Question

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

Answer 1

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