A boat goes 30 km upstream in 3 hours and downstream in 1 hour. How much time (in hours) will this boat take to cover 60 km in still water?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 3.
Let the speed of the boat be 'a' km/hr and the speed of the stream be 'b' km/hr
A boat goes 30 km upstream in 3 hours,
⇒ 30/(a - b) = 3
⇒ a - b = 10................(1)
A boat goes 30 km downstream in 1 hour,
⇒ a + b = 30/1 = 30........(2)
On solving eq (1) and (2) we get.
⇒ 2a = 40
⇒ a = 20 km/hr and b = 10 km/hr.
Time taken by boat to cover 60 km = 60/20 = 3 hours