Quantitative Aptitude Questions and Answers - Stream Boat Problems
11. A boat covers 12 km upstream and 18km downstream in 3hrs while it covers 18 km upstream and 12km
downstream in 3(1/4) hrs the velocity of the the boat upstream and downstream?
A. 12km/hr
B. 14km/hr
C. 16km/hr
D. 18km/hr
View Answer
Ans : A
Explanation: Let rate of upstream be 'x'km/hr and downstream be 'y' km/hr
Then, 12/x + 18/y = 3 -->1
18/x + 12/y =13/4 -->2
Adding 1 and 2 we get,
30/x + 30/y = 25/4
1/x + 1/y +=5/24 -->3
Subtracting 1 and 2 we get
1/x – 1/y = 1/24 -->4
Adding 3 and 4 we get,
2/x = 6/24 ; x= 8 ->5
Substitute 5 in 3 we get, y=12
Speed of upstream = 8 km/hr and downstream = 12 km/hr
12. A boat takes 24 hours to cover 128 km downstream and 16 hours to cover 64 km upstream. Then the speed of the boat in still water is:
A. 14/3
B. 8/7
C. 3/2
D. 9/5
View Answer
Ans : A
Explanation: Distance covered in downstream = 128km
Time taken in downstream = 24 hours.
Rate of downstream = distance / time = a = 128 km /24 hours = 16/3km/hr
Distance covered in upstream = 64km
Time taken in upstream = 16 hours.
Rate of upstream = distance / time = b = 64km /16hours = 4 km/hr.
Speed in still water = (a + b) / 2 = (1/2)(16/3+4) km/hr = (1/2)(28/3)km/hr
= 14/3km/hr
13. A boatman can take the same time to row6.5km downstream and 3.5km upstream. His
speed in still water 2.5 km/hr. The speed of the stream is:
A. 0.75km/hr
B. 2.5km/hr
C. 1.5km/hr
D. 7.5km/hr
View Answer
Ans : A
Explanation: Given that the speed in still water = 2.5 km/hr
Let the speed of the stream be 'x' km/hr
speed in upstream = (2.5 – x)km/hr
Then time taken to cover 6.5 km downstream = 6.5 / (2.5+x)
Then time taken to cover 3.5 km upstream = 3.5 / (2.5 – x)
6.5 / (2.5 + x) = 3.5 / (2.5 – x)
6.5 (2.5 – x) = 3.5 (2.5 + x)
16.25 – 6.5x = 8.75 + 3.5x
10 x = 7.5
x = 0.75 km/hr
The speed of the stream is 0.75 km/hr
14. A girl can row 15 kmph in still water and he finds that it takes him thrice as long to row up as to row down
the river. Find the rate of stream.
A. 4.5km/hr
B. 5.5km/hr
C. 6.5km/hr
D. 7.5km/hr
View Answer
Ans : D
Explanation: Given that, time taken to travel upstream = 3 × time taken to travel downstream
When distance is constant, speed is inversely proportional to the time
Hence, 3 × speed upstream = speed downstream
Let speed upstream =x
Then speed downstream =3x
we have, 1/2(x+3x) = speed in still water
i.e., 2x =15 -> x=7.5
i.e., speed upstream =7. 5 km/hr
Rate of stream =1/2(3x−x)= x = 7.5km/hr
15. A boat goes 3.5km upstream in 24 mins and the speed of the stream is 1.5km per hour,
then the speed of the boat in still water is.
A. 5.25kmph
B. 7.25kmph
C. 10.25kmph
D. 12.25kmph
View Answer
Ans : C
Explanation: Speed of upstream = 3.5 / 24 km/min
= 3.5 / 24 * 60 km/hr
= 8.75 km/hr
Speed of the stream = (1/2) (a – b)km/hr = 1.5 km/hr
1.5 = (1/2) ( a- 8.75)km/hr
a = 11.75 km/hr
speed of the boat in still water = (1/2)(a + b) km/hr
= (1/2) (11.75 + 8.75)
= (1/2)(20.5)
The speed of the boat in still water = 10.25 km/hr
16. A man can row 4 km against the stream in 40mins and return in 36mins. Find the rate of current.
A. 1/3kmph
B. 2/3kmph
C. 4/3kmph
D. 5/3kmph
View Answer
Ans : A
Explanation: Speed of the man (upstream) = (4 / 40 * 60) km/hr
= 6 km/hr
Speed of the man (downstream) = ( 4 / 36 * 60) km/hr
= (60 / 9)km/hr
= 20/3 km/h
Rate of the current = ½[downstream speed – upstream speed]
= (1/2) [ 20 / 3 – 6] km/hr
Rate of the current = 1/3 km/hr
17. A motor boat sails 30 km of a river towards upstream in 10hrs. How long will it take to
cover the same distance downstream, if the speed of the current is ½ of the speed of the boat
in still water.
A. 1.8hr
B. 3.33hr
C. 5hr
D. 4.33hr
View Answer
Ans : B
Explanation: Upstream speed = x –y
Downstream speed = x + y
x– y = 30/10 = 3km/hr
Again x = 2y
Therefore x – y = 3
y= 3km/hr ; x = 6km/hr
Therefore x + y = 9 km/hr
Time during downstream = 30/9 = 3.33hrs
18. Mohana can row 80km upstream and 110km downstream in 26 hrs. Also she can 60km upstream and
88km downstream in 20 hrs. Find the speed of the girl in still water and the speed of the current in ratio:
A. 5:6
B. 3:7
C. 7:9
D. 8:3
View Answer
Ans : D
Explanation: Let rate upstream = 'x' km/hr and
Rate downstream = 'y' km/hr
Then 80/x + 110/y = 26 --->1
60/x + 88/y = 20-->2
By solving 1 and 2
y= 11 ; x = 5
Rain in still water = (1/2) (11 + 5) km/hr = 8 km/hr
Rain of current = (1/2) (11 – 50) km/hr = 3 km/hr
The required answer is 8:3
19. A person can swim in water with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, what will be the time taken by the person to go 68 km downstream?
A. 1hr
B. 2hr
C. 3hr
D. 4hr
View Answer
Ans : D
Explanation: Downstream Speed = (13+4) km/hr = 17 km/hr
To travel 68 km downstream.
Time taken = 68/17 = 4 hours
20. A woman can row upstream at 16 km/hr and downstream at 26 km/hr. What is the speed of the stream?
A. 1km/hr
B. 5km/hr
C. 3km/hr
D. 9km/hr
View Answer
Ans : B
Explanation: According to the formula,
Speed of the stream = (1/2)(Downstream Speed – Upstream Speed)
Speed of the stream = (1/2)(26-16) = (1/2) × 10 = 5 km/hr
Discussion