Speed of motorboat in still water is 45 km/h. If the motorboat travels 80 km along the stream in 1 h 20 min, then the time taken by it to cover the same distance against the stream will be
Correct Answer: Description for Correct answer:
Let speed of stream be x km/h.
Given Speed of motorboat in still water = 45 km/h
Therefore, Speed of boat along stream = (45 + x) km/h
According to the question,
45 + x = \( \Large \frac{80}{1\frac{1}{3}} \)
= 45 + x = \( \Large \frac{80 \times 3}{4} \)
= x = 60 - 45 = 1 5
= Speed of boat against stream
= 45 - 15 = 30 km/h
Hence, required time = \( \Large \frac{Distance}{Speed} \)
= \( \Large \frac{80}{30}=\frac{8}{3} \times 60 = 160 min \) = 2 h 40 min
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