Solved UPSC CDS/OTA Question
A solved UPSC CDS/OTA PYQ - decoded step-by-step.
Solve it the standard way once - then learn the shortcut.
Q · Boat and StreamMedium · 45s
A boat sails down the river for 10 km and then up the river for 6 km. The speed of the river flow is 1 km/h. What should be the minimum speed of the boat for the trip to take a maximum of 4 hours?
TopicBoat and Stream
Question Typemultiple choice
DifficultyMedium
Marking+1 / −0.33
Test Duration30 min
Step-by-Step Solution
The complete worked solution.
Every step explained - no skipped algebra.
Let boat speed = x km/h, river = 1 km/h
Downstream: 10 / (x + 1)
Upstream: 6 / (x − 1)
Total time ≤ 4 hours
Equation:
10/(x + 1) + 6/(x − 1) ≤ 4
Try x = 4 → 10/5 + 6/3 = 2 + 2 = 4
Final Answer: Option C - 4 kmph