A motorboat in still water travels at speed of 36 kmph. It goes 56 km upstream in 1 hour 45 minutes. The time taken by it to cover the same distance down the stream will be:
A. 2 Hours 25 Minutes
B. 3 Hours
C. 1 Hours 24 Minutes
D. 2 Hours 21 Minutes
Answer: Option C
Solution(By Examveda Team)
1 hour 45 minutes = $$1 + \frac{{45}}{{60}}$$ = $$\frac{7}{4}$$ hours. Speed of the motorboat up-stream, $$\eqalign{ & = \frac{{{\text{Distance}}}}{{{\text{Time}}\,\,{\text{Taken}}}} \cr & = \frac{{56\,{\text{km}}}}{{\frac{7}{4}{\text{hours}}}} \cr & = \frac{{56 \times 4}}{7} \cr & = 32\,{\text{kmph}} \cr} $$ Let the speed of the current = x kmph Hence, 36 - x = 32 Or, x = 36 - 32 = 4 kmph Speed of boat down the stream = 36 + 4 = 40 kmph.∴ Time taken to cover 56 km at 40 kmph = $$\frac{{56}}{{40}}$$ = $$\frac{7}{5}$$ hours
or 1 hours 24 minutes.
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Related Questions on Speed Time and Distance
A. 48 min.
B. 60 min.
C. 42 min.
D. 62 min.
E. 66 min.
A. 262.4 km
B. 260 km
C. 283.33 km
D. 275 km
E. None of these
A. 4 hours
B. 4 hours 30 min.
C. 4 hours 45 min.
D. 5 hours
Upstream (s)=d/2=(56*4)/7=32kmph
Stillwater speed=(downstream+upstream)/2
or, downstream=(36×2)-32=40kmph
Downstream (T)=d/s=56/40=1.4h=1.4×60=84min=1h24min