The boat goes 30 km upstream and 44 km downstream in 10 hours. In 13 hours, it can go 40 km upstream and 55 km downstream. Determine the speed of stream and that of the boat in still water.
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 30 km upstream and 44 km downstream in 10 hours. In 13 hours, it can go 40 km upstream and 55 km downstream
------- (1)
Also, 
------ (2)
Multiplying eq1 by 4 and eq2 by 3 and (1) – (2)
⇒ a + b = 11 ------- (3)
Substituting value of (a + b) into eq1
⇒ a – b = 5 ------ (4)
From (1) and (2), we get
a = 8 km/hr and b = 3 km/hr
3