A person rows a distance of 20 km upstream and 15 km downstream in a total time of hours. If the speed of the current is 4 km/h, then in how many hours can he row a distance of 64 km upstream?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. .
Let boat speed in still water = x km/h
20/(x - 4) + 15/(x + 4) = 29/12
⇒ 29x2 - 420x - 704 = 0
⇒ x = [420 ± √[4202 - 4 × 29 × (-704)]/58
= [420 ± 508]/58
= (420 + 508)/58
= 16 km/h
Upstream speed = x - 4 = 16 - 4 = 12 km/h
Time for 64 km upstream = 64/12 = hours