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1.
In a stream running at 2 km/h, a motor boat goes 10 km upstream and back again to the starting point in 55 min. Find the speed of the motorboat in still water.
  • A.
    20 km/h
  • C.
    24 km/h
  • B.
    22 km/h
  • D.
    21 km/h
  • Answer & Explanation
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Answer : [B]
Explanation :
Let the speed of the motorboat in still water be x km/h
 
10
x + 2
+
10
x - 2
=
55
60
 
or, 240x = 11x2 - 44
or, 11x2 - 240x - 44 = 0
 
  (x - 22) (11x + 2) = 0  
So, x = 2 km/h (neglecting the negative value)
 
  Speed of the motorboat in still water = 22 km/h  
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2.
A man can row 6 km/h in still water. If the river is running at 2 km/h, it takes 3 hours more in upstream than to go downstream for the same distance. How far is the place?
  • A.
    36 km
  • C.
    28 km
  • B.
    24 km
  • D.
    None of these
  • Answer & Explanation
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Answer : [B]
Explanation :
The required distance =
(x2 - y2)t
2y
=
(36 - 4)3
2 x 2
 = 24 km      
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3.
Two boats, traveling 5 and 10 km/h, head directly towards each other. They begin at a distance of 20 kms from each other. How far apart are they (in kms) one minute before they collide?
  • A.
    1/3
  • C.
    1/4
  • B.
    1/6
  • D.
    1/12
  • Answer & Explanation
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Answer : [C]
Explanation :
In the final one minute before collision, the two boats travel 5 x
1
60
 km and 10 x
1
60
 km i.e.,
1
12
 
km and
1
6
 km, As they move in opposite directions, distance between the boats one minute before
collisions is
1
12
+
1
6
=
1
4
 km  
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4.
A boat goes 13 km upstream in 39 minutes. The speed of stream is 3 km/h. The speed of boat in still water is
  • A.
    27 km/h
  • C.
    23 km/h
  • B.
    25 km/h
  • D.
    None of these
  • Answer & Explanation
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Answer : [C]
Explanation :
Speed of the boat upstream =
13 x 60
39
 = 20 km/h
Speed of the stream = 3 km/h
Let the speed of the boat in still water = x km/h
We have, x 3 = 20
 
  x = 20 + 3 = 23 km/h  
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5.
A motor went the river for 14 km and then up the river for 9 km. It took a total of 5 hours the entire journey. Find the speed of the river flow if the speed of the boat in still water is 5 km/h.
  • A.
    3 km/h
  • C.
    2 km/h
  • B.
    1.5 km/h
  • D.
    1 km/h
  • Answer & Explanation
  • Report
Answer : [C]
Explanation :
Let the speed of the stream be x km/hours
Then Upward speed = (5 x) km/h and Downward speed = (5 + x) km/h
14
(5 + x)
+
9
(5 - x)
 = 5      
 
  x = 2 km/h  
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