A boat goes 15 km upstream in 1hr 20 mins. The speed of the stream is 4 kmph, the speed of boat in still water is :
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Solution
1 hour 20 minutes = 60+20 minutes = 80 minutes
= Speed of the boat in upstream = = 11.25 kmph
Upstream speed = speed of boat in still water- speed of water
Speed of boat in still water = (upstream speed + speed of water)
= 11.25 + 4 = 15.25 kmph
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?
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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.
A boat running in upstream takes 8 hours 48 minutes to cover a certain distance. While it takes 4 hours to cover the same distance running in downstream. What is the ratio between the speed of boat in still water and speed of stream ?
A man rows 18 km in upstream in 4 hours and also 27.5 km in downstream in 5 hours. The speed of the stream is :
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Solution
Speed in upstream = (18/4) = 4.50 kmph
Speed in downstream (27.5/5) = 5.5 kmph
Speed in of stream = (1/2) [(5.5) - (4.5)] = 0.5 kmph
A man takes 3 hours to row 21 km in downstream of a river and 1 hour to cover a distance of 5 km in upstream. Find the speed of the current.
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Solution
Speed in upstream = 5/1 = 5 km/hr
Speed in downstream = 21/3 = 7 km/hr
So, speed of current = (7 – 5) = 1 km/hr
If a man rows at the rate of 5 kmph in still water and his rate against the current is 3 kmph, then the man’s rate along the current is :
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Solution
Let the rate along with the current is x km/hr
⇒ x + 3 = 10
⇒ x = 7 kmph
A man can row 4 kmph in still water. If the speed of river is 2 kmph and he takes 90 min to row to a place and back. How far is the place?
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Solution
Speed of man in still water = 4 kmph
Speed of the stream = 2 kmph
Speed in upstream = (4-2) = 2 kmph
Speed in downstream = (4+2) = 6 kmph
Total time = 90 minutes = hours = hours
Let L be the distance. Then
= ⇒ L + 3L = 9
⇒ 4L = 9 ⇒ L =
⇒ 2.25 km
A boatman can row 96 km downstream in 8 hr. If the speed of the current is 4 km/hr, then find in what time he will be able to cover 8 km upstream?
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Solution
Speed in downstream = = 12 kmph
Speed of current = 4 km/hr
Speed of the boatman in still water = 12 – 4 = 8 kmph
Speed in upstream = 8 – 4 = 4 kmph
Time taken to cover 8 km upstream = = 2 hours
The speed of a boat in still water is 10 km/hr. If it can travel 78 km downstream and 42 km upstream in the same time, then the speed of the stream is :
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Solution
Let the speed of the stream be x km/hr. Then
Speed in upstream = (10 − x) km/hr
Speed in downstream = (10 + x) km/hr
Time taken to travel 78 km downstream = Time taken to travel 42 km upstream
⇒ 78/(10 + x) = 42/(10 − x)
⇒ 26 / (10 + x) = 14 / (10 − x)
⇒ 13 / (10 + x) = 7/ (10 − x)
⇒ 130 − 13 x = 70 + 7x
⇒ 20 x = 60
⇒ x = 3 km/hr
A boatman can row 3 km against the stream in 20 minutes and return in 18 minutes. Find the rate of current.
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Solution
Speed in upstream =
Speed in downstream = = 10 km/hr
Rate of current = km/hr