Boats and Streams


  1. A man rows 750 m in 600 seconds against the stream and returns in
    7
    1
    minutes
    2
    . Its rowing speed in still water is (in km/ hr).









  1. View Hint View Answer Discuss in Forum

    According to question ,

    Rate downstream =
    750
    m/minute
    15
    2

    Rate downstream = 100 m/minute
    Rate downstream =
    100 × 60
    kmph = 60kmph
    1000

    Rate upstream =
    750
    ×
    18
    kmph
    6005

    Rate upstream = 4.5 kmph
    ∴ Rowing speed in still water =
    1
    (6 + 4.5) =
    10.5
    = 5.25 kmph
    22

    Second method to solve this question :
    Here, p =
    750m
    15
    min
    2

    p =
    750 × 2 × 60
    = 6km/hr
    1000 × 15

    q =
    750 m
    =
    750 × 3600
    600s1000 × 600

    q = 4.5 km/hr

    Correct Option: D

    According to question ,

    Rate downstream =
    750
    m/minute
    15
    2

    Rate downstream = 100 m/minute
    Rate downstream =
    100 × 60
    kmph = 60kmph
    1000

    Rate upstream =
    750
    ×
    18
    kmph
    6005

    Rate upstream = 4.5 kmph
    ∴ Rowing speed in still water =
    1
    (6 + 4.5) =
    10.5
    = 5.25 kmph
    22

    Second method to solve this question :
    Here, p =
    750m
    15
    min
    2

    p =
    750 × 2 × 60
    = 6km/hr
    1000 × 15

    q =
    750 m
    =
    750 × 3600
    600s1000 × 600

    q = 4.5 km/hr
    ∴ Speed of Boat =
    1
    (p + q)
    2

    Speed of Boat =
    1
    (6 + 4.5) = 5.25 km/hr
    2


  1. A man rows upstream 36 km and downstream 48 km taking 6 hours each time. The speed of the current is









  1. View Hint View Answer Discuss in Forum

    As per the given in above question , we have

    Rate downstream of boat =
    48
    = 8 kmph
    6

    Rate upstream =
    36
    = 6 kmph
    6

    ∴ Speed of current =
    1
    (Rate down stream – rate upstream)
    2

    Speed of current =
    1
    (8 – 6) = 1 kmph
    2

    We can find the required answer with the help of given formula :
    Here, p =
    48
    = 8 kmph
    6

    q =
    36
    = 6 kmph
    6

    Correct Option: C

    As per the given in above question , we have

    Rate downstream of boat =
    48
    = 8 kmph
    6

    Rate upstream =
    36
    = 6 kmph
    6

    ∴ Speed of current =
    1
    (Rate down stream – rate upstream)
    2

    Speed of current =
    1
    (8 – 6) = 1 kmph
    2

    We can find the required answer with the help of given formula :
    Here, p =
    48
    = 8 kmph
    6

    q =
    36
    = 6 kmph
    6

    Speed of Current =
    1
    (p - q)
    2

    Speed of Current =
    1
    (8 - 6) = 1 kmph
    2



  1. A boat takes half time in moving a certain distance downstream than upstream. The ratio of the speed of the boat in still water and that of the current is









  1. View Hint View Answer Discuss in Forum

    Suppose Speed of boat in still water = p kmph
    Speed of current = q kmph
    Rate downstream = (p + q) kmph
    Rate upstream = (p – q) kmph
    Distance = Speed × Time
    ∴ (p – q) × 2t = (p + q) × t
    ⇒ 2p – 2q = p + q
    ⇒ 2p – q = 2q + q
    ⇒ p = 3q

    Correct Option: D

    Suppose Speed of boat in still water = p kmph
    Speed of current = q kmph
    Rate downstream = (p + q) kmph
    Rate upstream = (p – q) kmph
    Distance = Speed × Time
    ∴ (p – q) × 2t = (p + q) × t
    ⇒ 2p – 2q = p + q
    ⇒ 2p – q = 2q + q
    ⇒ p = 3q

    p
    =
    3
    = 3 : 1
    q1


  1. A man rows down a river 15 km in 3 hrs. with the stream and returns in 7
    1
    hrs,
    2
    The rate at which he rows in still water is









  1. View Hint View Answer Discuss in Forum

    Let speed of person in still water = p kmph and speed of current = q kmph

    ∴ p + q =
    15
    = 5 kmph ........( 1 )
    3

    & p – q =
    15
    15
    2

    p - q = 2 kmph ......( 2 )
    On adding equations ( 1 ) and ( 2 ) ,
    2p = 7 ⇒ p =
    7
    = 3.5 kmph
    2

    We can find the required answer with the help of given formula : :
    Here, p =
    15
    = 5 kmph
    3

    q =
    15
    15
    2

    q = 2 km/hr

    Correct Option: C

    Let speed of person in still water = p kmph and speed of current = q kmph

    ∴ p + q =
    15
    = 5 kmph ........( 1 )
    3

    & p – q =
    15
    15
    2

    p - q = 2 kmph ......( 2 )
    On adding equations ( 1 ) and ( 2 ) ,
    2p = 7 ⇒ p =
    7
    = 3.5 kmph
    2

    We can find the required answer with the help of given formula : :
    Here, p =
    15
    = 5 kmph
    3

    q =
    15
    15
    2

    q = 2 km/hr
    Speed of Boat =
    1
    (p + q)
    2

    Speed of Boat =
    1
    (5 + 2) = 3.5 kmph
    2



  1. The speed of a stream is 3 km/ hr. and the speed of a man in still water is 5 km/hr. The time taken by the man to swim 26 km downstream is :









  1. View Hint View Answer Discuss in Forum

    Given in question , Speed of a stream is 3 km/ hr and the speed of a man in still water = 5 km/hr

    Time =
    Distance
    Rate downstream

    Rate downstream = 5 + 3 = 8 kmph

    Correct Option: B

    Given in question , Speed of a stream is 3 km/ hr and the speed of a man in still water = 5 km/hr

    Time =
    Distance
    Rate downstream

    Rate downstream = 5 + 3 = 8 kmph
    Time =
    26
    =
    13
    = = 3
    1
    hours
    844