On any fixed stretch, a boat's downstream trip takes 20% less time than its upstream trip. If its speed in still water is 18 km/h, what is the speed of the current?
Competition practiceBoats & Streams
A2 km/h
B3.6 km/h
C1.8 km/h
D4 km/h
Step-by-Step Solution
tdown=0.8tup ⇒ D=1.25U.18+s=1.25(18−s) ⇒ 2.25s=4.5 ⇒ s=2 km/h.
Answer: A) 2 km/h
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