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Boat and Stream Questions with Solutions

Boat and Stream questions are Time, Speed and Distance questions wearing a different costume — convert the boat’s and stream’s speeds into a downstream or upstream speed first, then it’s the same formulas you already know. Here’s the concept, four fully worked examples, and a few to try yourself.

The concept, quickly

  • If a boat’s speed in still water is B and the stream’s speed is S: downstream speed (with the current) = B + S. Upstream speed (against the current) = B − S.
  • Given the downstream speed (D) and upstream speed (U), you can recover the boat’s and stream’s own speeds by reversing the formula: boat speed = (D + U) / 2, stream speed = (D − U) / 2.
  • Once you have a downstream or upstream speed, it’s an ordinary Time, Speed and Distance problem — apply Time = Distance / Speed as usual.
  • For a round trip covering the same distance downstream and back upstream, use the same two-unequal-speeds average-speed shortcut from Time, Speed and Distance: average speed = 2 × downstream speed × upstream speed / (downstream speed + upstream speed).

Worked examples

1. A boat’s speed in still water is 10 km/hr, and the speed of the stream is 4 km/hr. Find the boat’s downstream and upstream speeds.

Solution

  1. Downstream speed = boat speed + stream speed = 10 + 4 = 14 km/hr.
  2. Upstream speed = boat speed − stream speed = 10 − 4 = 6 km/hr.

Answer: Downstream = 14 km/hr, Upstream = 6 km/hr

2. A boat can row 24 km downstream in 2 hours. If the boat’s speed in still water is 9 km/hr, find the speed of the stream.

Solution

  1. Downstream speed = Distance / Time = 24 / 2 = 12 km/hr.
  2. Stream speed = downstream speed − boat speed = 12 − 9 = 3 km/hr.

Answer: 3 km/hr

3. A man can row 15 km upstream in 3 hours, and his speed in still water is 7 km/hr. Find the speed of the stream and the time he would take to cover the same 15 km downstream.

Solution

  1. Upstream speed = Distance / Time = 15 / 3 = 5 km/hr.
  2. Stream speed = boat speed − upstream speed = 7 − 5 = 2 km/hr.
  3. Downstream speed = boat speed + stream speed = 7 + 2 = 9 km/hr.
  4. Time downstream = Distance / Speed = 15 / 9 = 5/3 hours = 1 hour 40 minutes.

Answer: Stream speed = 2 km/hr, Time downstream = 1 hour 40 minutes

4. A boat’s downstream speed is 18 km/hr and its upstream speed is 12 km/hr. Find the boat’s speed in still water, the speed of the stream, and the boat’s average speed for a round trip covering the same distance each way.

Solution

  1. Boat speed = (downstream + upstream) / 2 = (18 + 12) / 2 = 15 km/hr.
  2. Stream speed = (downstream − upstream) / 2 = (18 − 12) / 2 = 3 km/hr.
  3. Average round-trip speed = 2 × 18 × 12 / (18 + 12) = 432 / 30 = 14.4 km/hr.

Answer: Boat speed = 15 km/hr, Stream speed = 3 km/hr, Average round-trip speed = 14.4 km/hr

Try these yourself

Work through these the same way, then check against the answer.

1. A boat’s speed in still water is 12 km/hr, and the speed of the stream is 3 km/hr. Find the boat’s downstream and upstream speeds.

Answer: Downstream = 15 km/hr, Upstream = 9 km/hr

2. A boat can row 32 km downstream in 4 hours. If the boat’s speed in still water is 6 km/hr, find the speed of the stream.

Answer: 2 km/hr

3. A boat’s downstream speed is 20 km/hr and its upstream speed is 10 km/hr. Find the boat’s average speed for a round trip covering the same distance each way.

Answer: 40/3 ≈ 13.33 km/hr

Where this comes up

Boat and Stream is tested directly in the Quantitative/Numerical Aptitude section of every exam Pariksha Saathi covers — SSC CGL, SSC MTS, SSC CHSL, IBPS PO, IBPS Clerk, SBI PO and SBI Clerk — as a direct extension of Time, Speed and Distance.

Practice more Boat and Stream questions

This page covers the concept and a handful of worked examples. Pariksha Saathi has full topic-wise practice sets for Boat and Stream (and every other Quant/Reasoning/English topic) with instant scoring and explanations — free, no account required.

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