Boats and Streams


  1. A swimmer's speed downstream is 11 km/h and speed of the stream is 1.5 km/h. Find the upstream speed of swimmer. ?









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    Rate of stream = ( Speed downstream - Speed upstream )/2

    Correct Option: A

    Rate of stream = ( Speed downstream - Speed upstream )/2
    ⇒ 1.5 = (11 - Speed upstream)/2
    ⇒ 11 - Speed upstream = 3
    ∴ Speed upstream = 11 - 3 = 8 km/h


  1. A boat goes 48 km downstream in 20 h. It takes 4 h more to cover the same distance against the stream. What is the speed of the boat in still water ?









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    Speed of boat in still water = (Speed downstream + Speed upstream)/2

    Correct Option: A

    Speed downstream = 48/20 = 2.4 km/h
    Speed upstream = 48/24 = 2 km/h
    ∴ Speed of boat in still water = (Speed downstream + Speed upstream)/2
    = (2.4 + 2)/2 = 4.4/2 = 2.2 km/h



  1. Keshav can row 60 km downstream and 36 km upstream, taking 10 h each time. What is the velocity of the current?









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    Velocity of the current = (speed downstream - Speed upstream)/2

    Correct Option: D

    Speed upstream = Distance/Time = 60/10 = 6 km/h
    Speed upstream = Distance/Time = 36/10 = 3.6 km/h
    ∴ Velocity of the current = (speed downstream - Speed upstream)/2
    = (6 - 3.2)/2 = 1.2 km/h


  1. What time will be taken by a boat to cover a distance of 128 km along the stream, if speed of a boat in still water is 24 km/h and speed of stream is 8 km/h?









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    Downstream speed of boat = Speed of boat in still water + Speed of stream
    Required time = Distance/Speed downstream

    Correct Option: A

    Downstream speed of boat = Speed of boat in still water + Speed of stream
    = 24 + 8 = 32 km/h
    ∴ Required time = Distance/Speed downstream
    = 128/32 = 4 km/h



  1. A boat goes 12 km upstream in 48 minutes. The speed of stream is 2 km/hr. The speed of boat in still water is ?









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    ∵ (12 x 60)/48 = (L - 2)

    Correct Option: C

    ∵ (12 x 60)/48 = (L - 2)
    ∴ L = 15 + 2 = 17 km/hr