9 kilometres may be covered by a speed boat in 2 hours in the lower direction of impact and in 6 hours in the direction of flow. What will the boat's speed (in kilometres per hour) and flow direction be then?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e 3 km/h and 1.5 km/h
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 the 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 ....(1)
Speed of the 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