A person rows a distance of (15/4)km upstream in (3/2) hours and a distance of 13 km downstream in 2 hours. How much time (in hours) will the person take to row a distance of 90 km in still water?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 20
Let the speed of the boat = x km/hr
speed of current = y km/hr
then upstream = (x - y) km/hr
downstream = (x + y) km/hr
so, according to the question
(15/4)/(x - y) = 1.5
⇒ x - y = 5/2
and 13/(x + y) = 2
⇒ x + y = 13/2
solving two equations, x = 9/2 and y = 2
so speed of the boat = 4.5 km/hr
speed of current = 2 km/hr
time taken for rowing = (90/4.5) = 20 hr