This question was previously asked in

Official Soldier GD Paper: [Rajput Regt Centre, Fategarh (Lucknow)] - 28 March 2021

Option 1 : 3 km / h and 1.5 km / h

Given:

A motor boat takes 2 h to travel a distance of 9 km down the current. It takes 6 h to travel the same against the current

Formula used:

Speed = Distance / Time

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

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

Calculation

Let the speed of boat in still water be x km/hr

Speed of current be y km/hr

Speed of boat downstream

⇒ x + y = 9/2

⇒ x + y = 4.5 km/hr - - (i)

Speed of boat against the current

⇒ x - y = 9/6

⇒ x - y = 1.5 km/hr - - (ii)

Solving equations i and ii

Add eqn i and ii we get

⇒ x = (4.5 + 1.5) / 2

⇒ x = 3 km/hr

Substracting eqn 1 from 2 we get

⇒ y = (4.5 - 1.5) / 2

⇒ y = 1.5 km/hr

Speed of boat in still water = 3 km/hr

Speed of boat against the current = 1.5 km/hr