In 4 hours, a boat goes 12 km along the stream. It covers 6 km against the stream in the same time. The speed of the boat in still water (in km/h) is:
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 2.25.
Let the speed of the boat be x and the speed of the stream be y;
Downstream Speed:
(x + y) = Distance/Time
⇒ (x + y) = 12/4 = 3 km/hr......(1)
Upstream Speed = Distance/Time
⇒ (x - y) = 6/4 = 3/2 km/hr.......(2)
On solving equations (1) and (2):
2x = 3 + 3/2
⇒ 2x = 9/2
⇒ x = 9/4 = 2.25
Hence,
Speed of the boat = 2.25 km/hr