Question

A boat goes 20 km downstream in one hour and the same distance upstream in two hours. What is the speed of the boat in still water?

Answer 1

Let the speed of the boat in still water be \(x\) km/hr and speed of the stream = y km/hr 

Then, speed of boat downstream = (\(x\) + y) km/hr 

Speed of boat upstream = (\(x\) – y) km/hr

Given (\(x\) + y) × 1 = 20 and (\(x\) – y) × 2 = 20 

⇒ \(x\) + y = 20            …(i)           and \(x\) – y = 10        …(ii) 

Adding eqn (i) and (ii), we get 

2\(x\) = 30  ⇒ \(x\) = 15 km/hr.