Boats and Streams

Boats and Streams

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Aptitude miscellaneous
  1. A man rows to a place 48 km distant and back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is ?








  1. View Hint View Answer Discuss in Forum

    Suppose he moves 4 km downstream in H hrs.
    Then, Speed downstream = 4/H km/hr
    Speed upstream = 3/H km/hr

    T1 + T2 = 14
    ∵ (48 x H)/4 + (48 x H)/3 = 14

    Correct Option: B

    Suppose he moves 4 km downstream in H hrs.
    Then, Speed downstream = 4/H km/hr
    Speed upstream = 3/H km/hr

    T1 + T2 = 14
    ∵ (48 x H)/4 + (48 x H)/3 = 14
    ⇒ 12H + 16H = 14
    ⇒ H = 1/2

    ∴ Speed downstream = 8 km/hr
    Speed upstream = 6 km/hr
    ∴ Rate stream = (8 - 6)/2 km/hr = 1 km/hr

  1. The current of a stream runs at 1 km/hr. A motor boat goes 35 km upstream and back again to the starting point in 12 hours. The speed of motor boat in still water is ?








  1. View Hint View Answer Discuss in Forum

    Let the speed in still water be x km/hr
    ∵ 35/(x - 1) + 35/(x + 1) = 12

    Correct Option: A

    Let the speed in still water be x km/hr
    ∵ 35/(x - 1) + 35/(x + 1) = 12
    ⇒ 35(2x) = 12(x2 - 1)
    ⇒ 12x2 - 70x - 12 = 0
    ⇒ 12x2 - 72x + 2x - 12 = 0
    ⇒ 12x(x - 6) + 2 (x - 6) = 0
    ⇒ (x - 6) (12x + 2) = 0
    ∴ x = 6 km/hr

  1. A man can row 91/3 in still water and he finds that it takes him thrice as much time to row up than as to row down the same distance in river. The speed of the current is ?








  1. View Hint View Answer Discuss in Forum

    Let speed upstream = x km/hr

    Then, speed downstream = 3x km/hr
    ∴ Speed in still water = (x + 3x)/2 km/hr = 2x km/hr

    Speed of the current = (3x - x)/2 km/hr = x km/hr

    Correct Option: D

    Let speed upstream = x km/hr

    Then, speed downstream = 3x km/hr
    ∴ Speed in still water = (x + 3x)/2 km/hr = 2x km/hr

    Speed of the current = (3x - x)/2 km/hr = x km/hr

    &becaus 2x = 28/3
    ∴ x = 14/3 = 42/3 km/hr.

  1. A man can row three quarters of a kilometre against the stream in 111/ 4 minutes and return in 71/ 2 minutes. The speed of the man in still water is ?








  1. View Hint View Answer Discuss in Forum

    Speed upstream = (3/4) x (4/45 x 60 km/hr = 4 km/hr
    Speed upstream = (3/4) x (2/15) x 60 km/hr = 6 km/hr

    Correct Option: D

    Speed upstream = (3/4) x (4/45 x 60 km/hr = 4 km/hr
    Speed upstream = (3/4) x (2/15) x 60 km/hr = 6 km/hr
    ∴ Speed in still water = (4 + 6)/2 km/hr = 5 km/hr

  1. A man can swim 3 km/hr in still water. If the velocity of the stream be 2 km/hr, the time taken by him to swim to a place 10 km upstream and back is ?








  1. View Hint View Answer Discuss in Forum

    Speed upstream = (3 - 2) km/hr = 1 km/hr
    Speed downstream = (3 + 2) km/hr = 5 km/hr

    Correct Option: D

    Speed upstream = (3 - 2) km/hr = 1 km/hr
    Speed downstream = (3 + 2) km/hr = 5 km/hr
    Total time taken = (10/1 + 10/5) hr = 12 hrs.