Example 1
A boat's speed in still water is 9 km/h and the stream flows at 1 km/h. The boat goes 60 km downstream. How long will the return trip upstream take?
Answer: B) 7.5 hours
Upstream speed = 9 − 1 = 8 km/h; time = 60/8 = 7.5 hours.
Boats and Streams questions for competitive exams: rules, worked examples and practice
Boats and streams questions combine a boat's speed in still water with the speed of the current. Going with the current adds the speeds; going against it subtracts them.
Key rules and formulas
- Downstream speed = boat speed + stream speed.
- Upstream speed = boat speed − stream speed.
- Boat speed = (downstream + upstream) ÷ 2; stream speed = (downstream − upstream) ÷ 2.
- Time = distance ÷ speed for each leg separately.
Common traps
- Averaging the two times instead of working each leg separately.
- Mixing km/h with m/s; convert with × 5/18 or × 18/5.
Where Boats and Streams is asked
- IBPS Clerk Prelims (Numerical Ability)
- IBPS PO Prelims (Quantitative Aptitude)
- RRB Group D (Mathematics)
- RRB NTPC CBT 1 (Mathematics)
- SBI Clerk Prelims (Numerical Ability)
- SBI PO Prelims (Quantitative Aptitude)
- SSC CGL Tier 1 (Quantitative Aptitude)
- SSC CGL Tier 2 (Mathematical Abilities)
- SSC CHSL Tier 1 (Quantitative Aptitude)
Worked examples
Example 2
A boat's speed in still water is 12 km/h and the stream flows at 1 km/h. The boat goes 52 km downstream. How long will the return trip upstream take?
Answer: D) 4.73 hours
Upstream speed = 12 − 1 = 11 km/h; time = 52/11 = 4.73 hours.
Example 3
A boat's speed in still water is 8 km/h and the stream flows at 4 km/h. The boat goes 36 km downstream. How long will the return trip upstream take?
Answer: B) 9 hours
Upstream speed = 8 − 4 = 4 km/h; time = 36/4 = 9 hours.
Frequently asked questions
What is Boats and Streams in competitive exams?
Boats and streams questions combine a boat's speed in still water with the speed of the current. Going with the current adds the speeds; going against it subtracts them.
Which exams ask Boats and Streams questions?
On MockBazaar, Boats and Streams questions appear in IBPS Clerk Prelims, IBPS PO Prelims, RRB Group D, RRB NTPC CBT 1, SBI Clerk Prelims, SBI PO Prelims, SSC CGL Tier 1, SSC CGL Tier 2, SSC CHSL Tier 1.
What is the most common mistake in Boats and Streams?
Averaging the two times instead of working each leg separately.