A man can row three-quarters of a kilometer against the stream in 11 1/4th…
2023
A man can row three-quarters of a kilometer against the stream in 11 1/4th minutes and down the stream in 7 1/2 minutes. The speed (in km/hr) of the man in still water is: In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
- A.
7
- B.
6
- C.
5
- D.
8
Attempted by 134 students.
Show answer & explanation
Correct answer: C
Solution:
Convert distance and times to hours: distance = 3/4 km = 0.75 km; upstream time = 11 1/4 min = 11.25 min = 11.25/60 hr = 0.1875 hr; downstream time = 7 1/2 min = 7.5 min = 7.5/60 hr = 0.125 hr.
Compute upstream speed (u - v): 0.75 km ÷ 0.1875 hr = 4 km/hr.
Compute downstream speed (u + v): 0.75 km ÷ 0.125 hr = 6 km/hr.
Speed in still water (u) = average of upstream and downstream speeds = (4 + 6)/2 = 5 km/hr.
Answer: 5 km/hr