A motor boat whose speed is 15 km/hr in still water goes 36 km upstream and…
2016
A motor boat whose speed is 15 km/hr in still water goes 36 km upstream and comes back to the starting point in 5 hours. Find the speed of the stream.
- A.
5 km/hr
5 किमी/घं. - B.
10 km/hr
10 किमी/घं. - C.
Can't determine
ज्ञात नहीं कर सकते - D.
3 km/hr
3 किमी/घं.
Attempted by 3 students.
Show answer & explanation
Correct answer: D
Let the speed of the stream be s km/hr.
Upstream speed is (15 - s) km/hr and downstream speed is (15 + s) km/hr.
The total time is 36/(15 - s) + 36/(15 + s) = 5 hours.
Solving this equation yields 5s^2 = 45, so s = 3 km/hr.