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.
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Formula Block
Memorise — 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
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Exam Patterns
What 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.
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)
Common Mistake: 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.
If boat speed < stream speed, upstream movement is impossible
Time ratio upstream:downstream = Downstream speed:Upstream speed
For equal time upstream and downstream, distances are in ratio of speeds
Questions Asked in Previous Exams
Real questions from SSC papers — 2015 to 2024 · Showing 3 of 5
Exam Q 12022Previous Year Pattern
A boat travels 48 km downstream in 3 hours and 48 km upstream in 6 hours. A swimmer can swim at a speed equal to the boat's speed in still water. If the swimmer swims 32 km downstream, how long (in hours) will it take?
Exam Q 22022Previous Year Pattern
A boat takes 4 hours to travel 60 km downstream and 5 hours to travel 50 km upstream. If the boat travels 84 km downstream and then immediately returns 84 km upstream, what is the total time taken (in hours)?
Exam Q 32022Previous Year Pattern
A boat covers a certain distance downstream in 8 hours and the same distance upstream in 12 hours. If a person rows a boat at a speed of 15 km/h in still water, what is the distance?
💪 Practice Questions (11) · Showing 3
Q 1easy
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?
Q 2easy
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?
Q 3easy
A boat covers the same distance downstream in 4 hours as it covers upstream in 6 hours. If the stream's speed is 4 km/h, what is the boat's speed in still water?