Quantitative Aptitude

Boat and Stream: Practice Questions with Answers

19 practice questions on Boat and Stream, with answers; most also have an explanation or a worked solution. Try each one before you open its answer.

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1. Q.1

   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.

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

   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.

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2. Q.2

   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.

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

   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.

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3. Q.3

   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.

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

   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.

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4. Q.4

   A boat covers 36 km upstream in 3 hours, and the same 36 km downstream in 2 hours. Find the boat’s speed in still water and the speed of the stream.

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   Answer: Boat speed = 15 km/hr, Stream speed = 3 km/hr

   Solution:

   1. Upstream speed = 36/3 = 12 km/hr. Downstream speed = 36/2 = 18 km/hr.
   2. Boat speed = (18 + 12)/2 = 15 km/hr.
   3. Stream speed = (18 − 12)/2 = 3 km/hr.

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5. Q.5

   A man rows downstream at 12 km/hr and upstream at 8 km/hr. He rows to a certain place and back, taking a total of 5 hours. Find the distance to that place.

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   Answer: 24 km

   Solution:

   1. Let the distance be d. Total time = d/12 + d/8 = 5.
   2. d(1/12 + 1/8) = d(2/24 + 3/24) = d(5/24) = 5.
   3. d = 5 × 24/5 = 24 km.

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6. Q.6

   A boat takes twice as long to go a certain distance upstream as it does to cover the same distance downstream. If the boat’s speed in still water is 15 km/hr, find the speed of the stream.

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   Answer: 5 km/hr

   Solution:

   1. Time upstream = 2 × time downstream for the same distance, so downstream speed = 2 × upstream speed, i.e. n = 2.
   2. Boat speed : stream speed = (n+1) : (n−1) = 3 : 1.
   3. Since boat speed = 15, stream speed = 15/3 = 5 km/hr.
   4. Check: downstream = 15+5 = 20, upstream = 15−5 = 10; downstream/upstream = 2, matching the time ratio.

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7. Q.7

   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.

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   Answer: 3 km/hr

   Solution:

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

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8. Q.8

   Using the boat and stream from the previous question (downstream 12 km/hr, upstream 6 km/hr), find its average speed for a round trip over equal distances.

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   Answer: 8 km/hr. 2×12×6/(12+6) = 144/18.

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9. Q.9

   A boat's speed in still water is 20 km/hr. It takes three times as long to row upstream as downstream for the same distance. Find the speed of the stream.

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   Answer: 10 km/hr. Boat:stream = (3+1):(3−1) = 4:2 = 2:1, so stream = 20/2.

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10. Q.10

    A man rows downstream at 15 km/hr and upstream at 9 km/hr. He rows to a place and back in a total of 4 hours. Find the distance to the place.

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    Answer: 22.5 km. d(1/15+1/9) = d(8/45) = 4, so d = 4×45/8.

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11. Q.11

    A boat covers 24 km upstream in 4 hours and the same distance downstream in 2 hours. Find the boat's speed in still water and the stream's speed.

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    Answer: Boat = 9 km/hr, Stream = 3 km/hr. Upstream = 6 km/hr, downstream = 12 km/hr.

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12. Q.12

    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.

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    Answer: 40/3 ≈ 13.33 km/hr

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13. Q.13

    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.

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

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14. Q.14

    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.

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    Answer: 2 km/hr

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15. Q.15

    A boat can row 10 km downstream in 2 hours. If the speed of the stream is 1 km/hr, find the boat's speed in still water.

    1. A 4 km/hr
    2. B 5 km/hr
    3. C 3 km/hr
    4. D 6 km/hr
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    Correct answer: (A) 4 km/hr

    Downstream speed = 10/2 = 5 km/hr. Boat speed = downstream speed − stream speed = 5 − 1 = 4 km/hr.

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16. Q.16

    A boat can row 24 km downstream in 2 hours. If the speed of the stream is 4 km/hr, find the boat's speed in still water.

    1. A 8 km/hr
    2. B 12 km/hr
    3. C 4 km/hr
    4. D 16 km/hr
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    Correct answer: (A) 8 km/hr

    Downstream speed = 24/2 = 12 km/hr. Boat speed = downstream speed − stream speed = 12 − 4 = 8 km/hr.

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17. Q.17

    A boat can row 20 km downstream in 2 hours. If the speed of the stream is 1 km/hr, find the boat's speed in still water.

    1. A 9 km/hr
    2. B 10 km/hr
    3. C 8 km/hr
    4. D 11 km/hr
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    Correct answer: (A) 9 km/hr

    Downstream speed = 20/2 = 10 km/hr. Boat speed = downstream speed − stream speed = 10 − 1 = 9 km/hr.

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18. Q.18

    A boat can row 20 km downstream in 1 hour. If the speed of the stream is 2 km/hr, find the boat's speed in still water.

    1. A 18 km/hr
    2. B 20 km/hr
    3. C 16 km/hr
    4. D 22 km/hr
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    Correct answer: (A) 18 km/hr

    Downstream speed = 20/1 = 20 km/hr. Boat speed = downstream speed − stream speed = 20 − 2 = 18 km/hr.

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19. Q.19

    A boat can row 8 km downstream in 1 hour. If the speed of the stream is 1 km/hr, find the boat's speed in still water.

    1. A 7 km/hr
    2. B 8 km/hr
    3. C 6 km/hr
    4. D 9 km/hr
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    Correct answer: (A) 7 km/hr

    Downstream speed = 8/1 = 8 km/hr. Boat speed = downstream speed − stream speed = 8 − 1 = 7 km/hr.

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