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  • Question
  • Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?


  • Options
  • A. 2 kmph
  • B. 4 kmph
  • C. 6 kmph
  • D. 8 kmph

  • Correct Answer
  • 4 kmph 

    Explanation

    Let the distance in one direction = k kms

    Speed in still water = 4.5 kmph

    Speed of river = 1.5

    Hence, speed in upstream = 4.5 - 1.5 = 3 kmph

    Speed in downstream = 4.5 + 1.5 = 6 kmph

    Time taken by Rajesh to row upwards = k/3 hrs

    Time taken by Rajesh to row downwards = k/6 hrs

    Now, required Average speed = Total   distance Total   speed   =   2 k k 3   +   k 6   =   2 k   x   18 6 k   +   3 k   =   4   kmph  

     

    Therefore, the average speed of the whole journey = 4kmph.


  • Boats and Streams problems


    Search Results


    • 1. A boatman can row 96 km downstream in 8 hr. If the speed of the current is 4 km/hr, then find in what time he will be able to cover 8 km upstream ?

    • Options
    • A. 1.5 hrs
    • B. 1 hrs
    • C. 2.5 hrs
    • D. 2 hrs
    • Discuss
    • 2. A boat travels 72 km downstream in 8 hours and 84 km upstream in 12 hours. Find the speed of the boat in still water and the speed of the water current ?

    • Options
    • A. 9 and 3 kmph
    • B. 6 and 7 kmph
    • C. 8 and 1 kmph
    • D. 7 and 2 kmph
    • Discuss
    • 3. If sum of upstream and downstream speed of a boat is 82 kmph, and the boat travels 105 km. upstream in 3 hr, Find the time taken by boat to cover 126 km downstream.

    • Options
    • A. 2.8 hrs
    • B. 2.7 hrs
    • C. 2.6 hrs
    • D. 2.5 hrs
    • Discuss
    • 4. In one hour, a boat goes 12 km/hr along the stream and 6 km/hr against the stream. The speed of the boat in still water (in km/hr) is:

    • Options
    • A. 9
    • B. 8
    • C. 7
    • D. 7.5
    • Discuss
    • 5. A motorboat can go 10 miles downstream on a river in 20 min. It takes 30 min for this boat to go back at the same 10 miles. Find the speed of the current ?

    • Options
    • A. 8 m/h
    • B. 5 m/h
    • C. 7 m/h
    • D. 6 m/h
    • Discuss
    • 6. Find the speed of stream if a boat covers 36 km in downstream in 6 hours which is 3 hours less in covering the same distance in upstream?

    • Options
    • A. 1.5 kmph
    • B. 1 kmph
    • C. 0.75 kmph
    • D. 0.5 kmph
    • Discuss
    • 7. A man can row against the current three fourth of a kilometer in 15 min and returns same distance in 10 min, then ratio of his speed to that of current?

    • Options
    • A. 5:1
    • B. 3:1
    • C. 4:1
    • D. 2:1
    • Discuss
    • 8. A man swims downstream 72 km and upstream 45 km taking 9 hours each time; what is the speed of the current ?

    • Options
    • A. 1 kmph
    • B. 3.2 kmph
    • C. 1.5 kmph
    • D. 2 kmph
    • Discuss
    • 9. A person can row 8 1/2 km an hour in still water and he finds that it takes him twice as long to row up as to row down the river. The speed of the stream ?

    • Options
    • A. 1.78 kmph
    • B. 2.35 kmph
    • C. 2.83 kmph
    • D. 3.15 kmph
    • Discuss
    • 10. Amith can row a boat d km upstream and the same distance downstream in 5 hours 15 minutes. Also, he can row the boat 2d km upstream in 7 hours. How long will it take to row the same distance 2d km downstream for Amith ?

    • Options
    • A. 4 hrs 10 min
    • B. 3 hrs 15 min
    • C. 3 hrs 30 min
    • D. 4 hrs 1 min
    • Discuss


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