Question

A motorboat goes downstream in river and covers a distance between two coastal town s in 5 hrs. It covers this distance upstream in 6 hrs. If the speed of the stram is 3 km/hr find the speed of the boat in still water?

Answer 1

speed of stream = 3 km/hr
let speed of boat = x km/hr

now speed of guy while traveling upstream = x-3 km/hr
and while going downstream = x +3 km/hr
A/Q  dis/x+3 = 5  ⇒ dis = 5(x+3)          .......(1)
similarly dis/x-3 = 6 ⇒ dis = 6(x-3)              ........(2)

   ⇒  5x + 15 = 6x -18 ⇒ x = 33 km/hr

hope my ans to be correct.

Answer 2

Let the speed of the boat in still water = xkm/hrxkm/hr

Speed of the boat downstream =(x+3)km/hr=(x+3)km/hr

Time taken to cover the distance = 5 hrs

Distance covered in 5 hrs =(x+3)×5=(x+3)×5

Speed of the boat up stream =(x−3)km/hr=(x−3)km/hr

Time taken to cover the distance = 6 hrs

Distance covered in 5 hrs =6(x−3)=6(x−3)

Distance between two coastal towns is fixed .

According to the question

=> 5(x+3)=6(x−3)5(x+3)=6(x−3)

=> 5x+15=6x−185x+15=6x−18

=> −x=−33−x=−33

x=33x=33

Required speed of the boat is 33km/hr33km/hr

Answer : 33km/hr