Question : A man rows a boat a certain distance downstream in 9 hours, while it takes 18 hours to row the same distance upstream. How many hours will it take him to row three-fifths of the same distance in still water?
Option 1: 9.5
Option 2: 7.2
Option 3: 10
Option 4: 12
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Correct Answer: 7.2
Solution : Given: Time taken for upstream = 18 hours Time taken for downstream = 9 hours LCM of 9 and 18 is 18. Let the distance be 18 km. Downstream speed = $\frac{\text{Distance}}{\text{Time}}$ = $\frac{18}{9}$ = 2 km/hr Upstream speed = $\frac{18}{18}$ = 1 km/hr Speed of the boat in still water = $\frac{1+2}{2}$ = $\frac{3}{2}$ = 1.5 km/hr Now, $\frac{3}{5}$th of 18 km = $\frac{3}{5}\times 18$ = $\frac{54}{5}$ km Thus, the boat can row $\frac{54}{5}$ km with a speed of 1.5 km/hr = $\frac{\frac{54}{5}}{1.5}$ = $\frac{54}{7.5}$ = 7.2 hours Hence, the correct answer is 7.2.
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Question : A boat covers a distance of 80 km downstream in 8 hours, while it takes 10 hours to cover the same distance upstream. What is the speed (in km/hr) of the boat in still water?
Question : A boat running upstream takes 10 hours to cover a certain distance, while it takes 7 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and that of the water current, respectively?
Question : A man takes 15 minutes to row 16 km downstream, which is 25% less than the time he takes to row the same distance upstream. How many kilometres can the man row in an hour in still water? (Rounded off to the nearest whole number)
Question : To go a distance of 144 km upstream, a rower takes 12 hours while it takes her only 9 hours to row the same distance downstream. What is the speed of the stream?
Question : A boat goes 4 km upstream and 4 km downstream in an hour. The same boat goes 5 km downstream and 3 km upstream in 55 minutes. What is the speed (in km/hr) of the boat in still water?
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