6.
A boatman can row 48 km downstream in 4 hr. If the speed of the current is 5 km/hr, then find in what time will he be able to cover 8 km upstream?
• A.
6 h
• C.
8 h
• B.
4 h
• D.
None of these
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Explanation :
Speed of the boatman downstream =
 48 4
= 12 km/h
Speed of the current = 5 km/h
Let the boatman takes t hours to cover 8 km upstream.
Then, speed of the current =
 1 2
(Downstream Speed � Upstream Speed)
5 =
 1 2
12 -
 8 t

t = 4 hours

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7.
A boat, while going downstream in a river covered a distance of 50 miles at an average speed of 60 miles per hour. While returning because of the water resistance, it took one hour fifteen minutes to cover the same distance. What was the average speed during the whole journey?
• A.
40 mph
• C.
55 mph
• B.
48 mph
• D.
50 mph
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Explanation :
Time taken by boat in down stream =
 50 60
=
 5 6
h
Time taken by boat in upstream =
 5 4
h
 Average speed =
2 x 50
 5 6
+
 5 4
 =
 100 x 24 50
 = 48 mph

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8.
A man can row with the stream at 7 km/h and against the stream at 3 km/h. His soeed in still water is
• A.
7 km/h
• C.
6.5 km/h
• B.
5 km/h
• D.
None of these
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Explanation :
Speed of the man upstream = 7 km/h
Speed of the man downstream = 3 km/h
Speed of the man in still water =
 1 2
(Downstream Speed + Upstream speed)
=
 1 2
(7 + 3) = 5 km/h
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9.
In a stream that is running at 2 km/h, a man goes 10 km upstream and comes back to the starting point in 55 minutes. Find the speed of the man in still water.
• A.
28 km/h
• C.
22 km/h
• B.
20 km/h
• D.
24 km/h
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Explanation :
Let the speed of the man in still water be x km/h.
Then
 10 (x - 2)
+
 10 (x + 2)
=
 55 60

x = 22 km/h
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10.
A boat goes 40 km upstream in 8 hours and 36 km downstream in 6 hours. The speed of the boat in still water in km/hr is
• A.
5.5
• C.
6.6
• B.
4.5
• D.
None of these
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Explanation :
Boat�s upstream =
 40 8
= 5 km/h
Boat�s downstream speed =
 36 6
= 6 km/h
Speed of boat in still water =
 5 + 6 2
= 5.5 km/h
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