A person rows a distance of 3(3/4) km upstream in 1(1/2) hours and a distance of 13 km downstream in 2 hours. How much time (in hours) will the person take to draw a distance of 90 km in still water?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 20
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Let the speed of the boat in still water = x km/hr Speed of stream = y km/hr Now, Speed of rowing during upstream = (x-y) Km/hr Speed of rowing during downstream = (x+y) km/hr Given that a person rows a distance of 3(3/4) km upstream in 1(1/2) hours Speed of rowing during upstream = (15/4)/(3/2) = 2.5km/hr x - y = 2.5………………..(1) Also, the same person rows a distance of 13 km downstream in 2 hours Speed of rowing during downstream = 13/2 = 6.5 Km/hr x + y = 6.5 Km/hr…………………(2) Adding (1) and (2) 2x = 9 x = 4.5 km/hr Hence the speed of rowing in still water = 4.5 km/hr Now, he has to cover a distance of 90 km. Hence, Time required = (90/4.5) = 20 hr |