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Quiz: Boats and Streams

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Number of Questions: 40

Question: 21 -

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

Options:

  1. 6 kmph 

  2. 5.5 kmph

  3. 7.5 kmph 

  4. 8 kmph 

    5. Answer:

    6 kmph 
    Solution:

    Speed of the stream = 1
    Motor boat speed in still water be = x kmph
    Down Stream = x + 1 kmph
    Up Stream = x - 1 kmph
    [35/(x + 1)] + [35/(x - 1)] = 12
    x = 6 kmph

Question: 22 -

A boat sails 15 km of a river towards upstream in 5 hours. How long will it take to cover the same distance downstream, if the speed of current is one-fourth the speed of the boat in still water:

Options:

  1. 5h 

  2. 1.8h 

  3. 4h 

  4. 3h 

    5. Answer:

    3h 
    Solution:

    Upstream speed = B-S

    Downstream speed = B+s

    B-S = 15/5 = 3 km/h

    Again          B= 4S

    Therefore    B-S = 3= 3S

    =>             S = 1 and B= 4 km/h

    Therefore    B+S = 5km/h

    Therefore, Time during downstream = 15/5 = 3h

Question: 23 -

A boat takes 19 hours for travelling downstream from point A to point B and coming back to a point C which is at midway between A and B. If the velocity of the stream is 4 kmph and the speed of the boat in still water is 14 kmph, what is the distance between A and B ?

Options:

  1. 180 km 

  2. 140 km 

  3. 160 km

  4. 120 km 

    5. Answer:

    180 km 
    Solution:

    Speed in downstream = (14 + 4) km/hr = 18 km/hr;

    Speed in upstream = (14 – 4) km/hr = 10 km/hr.

    Let the distance between A and B be x km. Then,

    x/18 + (x/2)/10 = 19 ⇔ x/18 + x/20 = 19 ⇒ x = 180 km.

Question: 24 -

A boy can swim in still water at 4.5 km/h, but takes twice as long to swim upstream than downstream. The speed of the stream is ?

Options:

  1. 1.5 kmph 

  2. 2.2 kmph 

  3. 1.8 kmph 

  4. 2 kmph 

    5. Answer:

    1.5 kmph 
    Solution:

    Speed of Boy is B = 4.5 kmph

    Let the speed of the stream is S = x kmph

    Then speed in Down Stream = 4.5 + x

    speed in Up Stream = 4.5 - x

    As the distance is same,

    => 4.5 + x = (4.5 - x)2

    => 4.5 + x = 9 -2x

    3x = 4.5

    x = 1.5 kmph

Question: 25 -

A man can row 6 kmph in still water. When the river is running at 1.2 kmph, it takes him 1 hour to row to a place and back. What is the total distance traveled by the man ?

Options:

  1. 5.76 kms 

  2. 4.58 kms 

  3. 6.35 kms 

  4. 5.24 kms 

    5. Answer:

    5.76 kms 
    Solution:

    Speed in still water = 6 kmph

    Stream speed = 1.2 kmph

    Down stream  = 7.2 kmph

    Up Stream = 4.8 kmph

    x/7.2 + x/4.8 = 1

    x = 2.88

    Total Distance  = 2.88 x 2 = 5.76 kms