This page covers SSC GD Constable Boats & Streams with complete concept notes, 15 graded practice MCQs, key points and exam-specific tips. Free to study.
Core ConceptRead this first — the foundation of the topic
Core Concept
Imagine walking on a moving escalator. If you walk in the same direction as the escalator, you move faster. If you walk against it, you move slower. Similarly, water current helps or hinders boat movement
Key Rules
Speed of boat in still water = (Downstream speed + Upstream speed) ÷ 2. Speed of current = (Downstream speed - Upstream speed) ÷ 2. Downstream speed = Boat speed + Stream speed. Upstream speed = Boat speed - Stream speed.
Formula BlockMemorise — at least one formula appears in every paper
• Downstream Speed = Speed in still water + Speed of stream
• Upstream Speed = Speed in still water - Speed of stream
• Speed in still water = (Downstream + Upstream) ÷ 2
• Speed of stream = (Downstream - Upstream) ÷ 2
• Time = Distance ÷ Speed
Exam PatternsWhat examiners ask — read before attempting PYQs
Questions typically ask for boat speed in still water, stream speed, time calculations, or distance problems. Common formats include round trips, meeting point problems, and comparative speed questions.
ShortcutsUse these to save 30–60 seconds per question
When distance is same upstream and downstream, use the harmonic mean formula: Average speed = (2 × Downstream speed × Upstream speed) ÷ (Downstream speed + Upstream speed).
Worked ExampleSolve this step-by-step before moving on
Apply formulas
Boat speed in still water = (10 + 4) ÷ 2 = 7 km/hr
Stream speed = (10 - 4) ÷ 2 = 3 km/hr
Worked Example 2: A man can row 6 km/hr in still water. Stream speed is 2 km/hr. How long to travel 16 km downstream and return?
Calculate times
Time downstream = 16 ÷ 8 = 2 hours
Time upstream = 16 ÷ 4 = 4 hours
Total time = 2 + 4 = 6 hours
Trick for Round Trips: Total time = Distance × 2 × Boat speed ÷ (Boat speed² - Stream speed²)
Exam TrapsCommon mistakes students make — avoid these
Students often confuse downstream and upstream directions. Remember: downstream means 'with the flow' (faster), upstream means 'against the flow' (slower). Another trap is adding stream speed when calculating upstream speed instead of subtracting it.
Always check if your downstream speed is greater than upstream speed.
A boat's speed in still water is 12 km/h. It takes 5 hours to travel 50 km upstream. What is the speed of the stream?
Practice 2easy
A boat travels 48 km downstream in 3 hours. If the speed of the stream is 2 km/h, what is the speed of the boat in still water?
Practice 3easy
A boat's speed in still water is 10 km/h and the stream's speed is 3 km/h. How long will it take the boat to travel 91 km upstream?
Practice 4easy
A boat travels 72 km downstream in 4 hours and the same distance upstream in 9 hours. What is the speed of the boat in still water?
Practice 5easy
A boat covers 60 km downstream in 4 hours and 60 km upstream in 6 hours. What is the speed of the stream?
Practice 6easy
A man can row 24 km downstream in 2 hours. If his rowing speed in still water is 8 km/h, what is the speed of the current?
Practice 7medium
The speed of a boat in still water is 15 km/h and the speed of the current is 3 km/h. How long will it take the boat to travel 72 km downstream and then return to the starting point?
Practice 8medium
A boat travels 60 km downstream in 3 hours and 60 km upstream in 5 hours. If the boat travels 120 km in still water (no current), how long will it take?
Practice 9medium
A man can row 30 km upstream in 5 hours. If the speed of the current is 2 km/h, what is the speed of the man in still water?
Practice 10medium
A boat travels 48 km downstream in 3 hours and 48 km upstream in 6 hours. What is the speed of the boat in still water?
Practice 11hard
A boat covers a distance of 64 km in 4 hours downstream and the same distance in 8 hours upstream. A man can row at the speed of the boat in still water. If the man rows for 3 hours downstream and then 2 hours upstream in the same river, what is the total distance covered?
Practice 12hard
A boat takes 5 hours to travel 100 km downstream. The ratio of downstream speed to upstream speed is 5:3. If a person swims at 1/5th of the boat's still-water speed, how far can the person swim in 4 hours in still water?
Practice 13hard
A boat travels from port A to port B (120 km apart) downstream in 4 hours. On the return journey upstream, it takes 6 hours. A second boat, whose speed in still water is 2 km/h more than the first boat, travels the same route. How much time will the second boat take to travel from A to B downstream?
Practice 14hard
A man rows a boat 36 km downstream and returns upstream to the starting point. The total time taken is 8 hours. If the speed of the boat in still water is 10 km/h, what is the speed of the stream?
Practice 15hard
A boat's speed in still water is 20 km/h. The boat takes 2 hours to travel from point A to point B downstream and 3 hours to return upstream. If the boat travels the same distance in still water (no current), how much time will it take?