A boat running upstream takes 8 hours 48 minutes to cover a certain distance, while it takes 4 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the water current respectively?
Man’s speed with the current = 15 km/hr
=> speed of the man + speed of the current = 15 km/hr
speed of the current is 2.5 km/hr
Hence, speed of the man = 15 – 2.5 = 12.5 km/hr
man’s speed against the current = speed of the man – speed of the current
= 12.5 – 2.5 = 10 km/hr
Workspace
A man rows to a place 48 km distant and come 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:
A man takes 3 hours 45 minutes to row a boat 15 km downstream of a river and 2 hours 30 minutes to cover a distance of 5 km upstream. Find the speed of the current.
First of all, we know that
speed of current = 1/2(speed downstream – speed upstream)
So we need to calculate speed downstream and speed upstream first.
Speed = Distance / Time
Workspace
A boat travels upstream from B to A and downstream from A to B in 3 hours. If the speed of the boat in still water is 9km/hr and the speed of the current is 3km/hr, the distance A and B is:
A motorboat went the river for 14 km and then up the river for 9 km. If took a total of 5 hrs the entire journey. Find the speed of the river flow if the speed of the boat in still water is 5 km/h.
In a river flowing at 2 km/hr, a boat travels 32 km upstream and then returns downstream to the starting point. If its speed in still water be 6 km/hr, find the total journey time.
Total time taken = Time taken downstream + Time taken upstream
Workspace
A motorboat takes half time to cover a certain distance downstream than upstream. What is the ratio between rate of current and rate of boat in still water?
A man takes twice as long to row a distance against the stream as to row the same distance in favor of the stream. The ratio of the speed of the boat in still water and stream is
Let speed downstream = x kmph
Then Speed upstream = 2x kmph
So ratio will be,
(2x+x)/2 : (2x-x)/2
=> 3x/2 : x/2 => 3:1
Workspace
A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationary water?
A Ship of Length 300m traveling from point A to B downstream passes a Ghat along the river in 18 sec, while in return it passes the same Ghat in 24 sec. If the rate of current is 9 Km/hr. Then what is the length of the Ghat?
(S+9)*18 = (S-9)*24
S =63
300+x = 72*5/18*18
x =60
Workspace
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A boat can travel with a speed of 16 km/hr in still water. If the rate of the stream is 5 km/hr, then find the time taken by the boat to cover the distance of 84 km downstream.
It is very important to check, if the boat speed given is in still water or with water or against water. Because if we neglect it we will not reach on right answer. I just mentioned here because mostly mistakes in this chapter are of this kind only.
Lets see the question now.
Speed downstream = (16 + 5) = 21 kmph
Time = distance/speed = 84/21 = 4 hours
Workspace
Find the rate of the stream, if a boat covers 120 km downstream and 40 km upstream in 4 hours.
Distance covered in downstream = 120 km
Time taken in downstream = 4 hours.
Rate of downstream = distance / time = a = 120km / 4 hours = 30 km/hr.
Distance covered in upstream = 40 km
Since it takes same time to cover this 40km,
Time taken in upstream = 4 hours.
Rate of upstream = distance / time = b = 40km / 4 hours = 10 km/hr.
Speed of stream = (a – b)/2 = (1/2)(30 – 10) km/hr = 10 km/hr.
