A boat goes 24 km upstream and 28 km downstream in 6 hrs. It goes 30 km upstream and 21 km downstream in hrs. Find the speed of the boat in still water and also speed of the stream.

Speed = distance/time


Let the speed of boat be ‘a’ and speed of stream be ‘b’


Relative speed of boat going upstream = a – b


Relative speed of boat going downstream = a + b


Given, boat goes 24 km upstream and 28 km downstream in 6 hrs. It goes 30 km upstream and 21 km downstream in hrs


------- (1)


Also, ------ (2)


Multiplying eq1 by 3 and eq2 by 4 and (1) – (2)



a - b = 6 ------- (3)


Substituting value of (a - b) into eq1



a + b = 14 ------ (4)


From (1) and (2), we get


a = 10 km/hr and b = 4 km/hr


4