Question

A boat takes 9 hours to travel a distance upstream and takes 3 hours to travel the same distance downstream. If the speed of the boat in still water is 4 km /hr , what is the speed of the stream?

Answer 1

Answer:

Upstream = T = 9 hours

Downstream = T = 3 hours

Speed of the boat in still water = 4 km/hr

Let the speed of the stream be = x km/hr

Speed of the boat upstream = ( x - 4 ) km/hr

Speed of the boat downstream = ( x + 4 ) km/hr

Distance travelled upstream = 9 ( 4 - x ) km

Distance travelled downstream = 3 ( 4 + x )km

According to the question,

9 ( 4 - x ) = 3 ( 4 + x )

36- 9x = 12 + 3x

-9x - 3x = 12 - 36

- 12x = - 24

x = 24

12

Both cut & the answer is

x = 2 km /hr ( speed of the stream )