Question

A boat takes 3hours to go 45km downstream and it returns in 9hours .find the speed of the steam and that of boat in still water

Answer 1

Ans. Let Speed of boat in still water = x km/h

Speed of stream = y km/h

According to question, 

Case 1 Downstream :

Time taken = 3 hours

total distance = 45 km 

Speed of  boat downstream = x + y 

So, 453=x+y453=x+y

=> x+y = 15    ............. (1)

Case 2 Upstream : 

Time taken = 9 hours

total distance = 45 km 

Speed of  boat upstream = x - y 

So, 459=x−y459=x−y

=> x -  y = 5   ..............(2)

Adding (1) and (2) we get

=> 2x = 20 

x = 10 

From (2). 10 - y =  5 

=> y = 5 

So speed of boat in still water = 10 Km/h

Speed of stream = 5 Km/h