BOATS AND STREAMS EXAMPLE QUESTIONS
1) The speed of a boat in still water is 5km/hr. If the speed of the boat against the stream is 3 km/hr, what is the speed of the stream?
A)1.5 km/hr
B)2 km/hr
C)2.5 km/hr
D)1 km/hr
The correct answer is B
Answer with explanation:
Let the speed of stream = X km/hr
Speed of boat = 5 km/hr
Speed upstream = 3km/hr
Apply formula: Speed upstream = speed of boat - speed of stream
∴ 3 = 5 - X
2) A man rows downstream at 20 km/hr and rows upstream at 15 km/hr. At what speed he can row in still water?
A)17.5 km/hr
B)18 km/hr
C)20.5 km/hr
D)22 km/hr
The correct answer is A
Apply formula: Speed in still water = (1/2)(speed downstream + speed upstream)
Speed downstream = 20 km/hr
Speed upstream = 15 km/hr
∴ Required speed = (1/2)(20 + 15) km/hr
= (1/2)∗ 35 = 17.5 km/hr
3) A man can row a boat at a speed of 20 km/hr in still water. If the speed of the stream is 5 km/hr, in what time he can row a distance of 75 km downstream?
A)1.5 hours
B)2 hours
C)2.5 hours
D)3 hours
The correct answer is D
Answer with explanation:
Speed of boat = 20 km/hr
Speed of stream = 5 km/hr
∴ Speed downstream = 20 + 5= 25 km/hr
Required Time = Distance/time = 75/25 = 3 hours
4)A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
A.2 hours
B.3 hours
C.4 hours
D.5 hours
Answer: Option C
Explanation:
Speed downstream = (13 + 4) km/hr = 17 km/hr.
Time taken to travel 68 km downstream = 68/1700 hrs = 4 hrs.
5)A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:
A.8.5 km/hr
B.9 km/hr
C.10 km/hr
D.12.5 km/hr
Answer: Option C
Explanation:
Man's rate in still water = (15 - 2.5) km/hr = 12.5 km/hr.
Man's rate against the current = (12.5 - 2.5) km/hr = 10 km/hr.
6)A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:
A.4
B.5
C.6
D.10
Answer: Option B
Explanation:
Let the speed of the stream be x km/hr. Then,
Speed downstream = (15 + x) km/hr,
Speed upstream = (15 - x) km/hr.
30 / (15 + x) + 30 / (15 - x) = 4 1/2
900 / (225 - x^2) = 9/2
9x^2 = 225
x^2 = 25
x = 5 km/hr.
7)The speed of a boat in still water in 15km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is:
A.1.2 km
B.1.8 km
C.2.4 km
D.3.6 km
Answer: Option D
Explanation:
Speed downstream = (15 + 3) kmph = 18 kmph.
Distance travelled = (18 x 12/60) km = 3.6 km.
8)A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
A.2 mph
B.2.5 mph
C.3 mph
D.4 mph
Answer: Option A
Explanation:
Let the speed of the stream x mph. Then,
Speed downstream = (10 + x) mph,
Speed upstream = (10 - x) mph.
36 / (10 - x) - 36 /(10 + x) = 90/60
72x x 60 = 90 (100 - x^2)
x^2 + 48x - 100 = 0
(x+ 50)(x - 2) = 0
x = 2 mph.
9)A man can row at 5 kmph in still water. If the velocity of current is 1 kmph and it takes him 1 hour to row to a place and come back, how far is the place?
A.2.4 km
B.2.5 km
C.3 km
D.3.6 km
Answer: Option A
Explanation:
Speed downstream = (5 + 1) kmph = 6 kmph.
Speed upstream = (5 - 1) kmph = 4 kmph.
Let the required distance be x km.
Then, x/6 + x/4 = 1
2x + 3x = 12
5x = 12
x = 2.4 km.
10) A boat covers a certain distance downstream in 1 hour, while it comes back in 1 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?
A.12 kmph
B.13 kmph
C.14 kmph
D.15 kmph
E.None of these
Answer: Option D
Explanation:
Let the speed of the boat in still water be x kmph. Then,
Speed downstream = (x + 3) kmph,
Speed upstream = (x - 3) kmph.
(x + 3) x 1 = (x - 3) x 3/2
2x + 6 = 3x - 9
x = 15 kmph.
11)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.40 minutes
B.1 hour
C.1 hr 15 min
D.1 hr 30 min
Answer: Option C
Explanation:
Rate downstream = (1/10 x 60) km/hr = 6 km/hr.
Rate upstream = 2 km/hr.
Speed in still water = (1/2)(6 + 2)km/hr = 4 km/hr.
Required time = 5/4 hrs = 1 1/4 hrs = 1 hr 15 min.
12)A man can row three-quarters of a kilometre against the stream in 11 minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:
A.2
B.3
C.4
D.5
Answer: Option D
Explanation:
We can write three-quarters of a kilometre as 750 metres,
and 11 1/4 minutes as 675 seconds.
Rate upstream = 750/675 m/sec =10/9 m/sec.
Rate downstream = 750/450 m/sec = 5/3 m/sec.
Rate in still water = (1/2)( 10/9 + 5/3) m/sec
= 25/18 m/sec
= 25/18 x 18/5 km/hr
= 5 km/hr.
13)Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:
A.16 hours
B.18 hours
C.20 hours
D.24 hours
Answer: Option D
Explanation:
Speed upstream = 7.5 kmph.
Speed downstream = 10.5 kmph.
Total time taken = ( 105/7.5 + 105/10.5) hours = 24 hours.
14).A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is:
A.2 : 1
B.3 : 1
C.3 : 2
D.4 : 3
Answer: Option B
Explanation:
Let man's rate upstream be x kmph.
Then, his rate downstream = 2x kmph.
(Speed in still water) : (Speed of stream) = (2x + x) /2 : (2x - x) / 2
= 3x/2 : x/2
= 3 : 1.
15)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.1 km/hr
B.1.5 km/hr
C.2 km/hr
D.2.5 km/hr
Answer: Option A
Explanation:
Suppose he move 4 km downstream in x hours. Then,
Speed downstream = 4/x km/hr.
Speed upstream = 3/x km/hr.
48 / (4/x) + 48 / (3/x) = 14 or x = 1/2
So, Speed downstream = 8 km/hr, Speed upstream = 6 km/hr.
Rate of the stream = (1/2)(8 - 6) km/hr = 1 km/hr.
16) A man takes 20 minutes to row 12 km upstream which is a third more than the time he takes on his way downstream. What is his speed in still water?
A. 41 km/hr B. 36 km/hr C. 42 km/hr D. 45 km/hr
Sol : Option C
Let the speed in still water = x km/hr. Takes 20 min. to row 12 km upstream ⇒ speed of u/s = 36 km/hr. Also, time taken for u/s is 1/3 more than for d/s.
∴ distance covered in d / s will be 1/3 more.
Hence distance covered by man for d / s in 20 min. = 12 × (12/3) = 16km.
So speed of d / s = 48 km/hr.
∴ x + y = 48 and x – y = 36 ⇒ x = 42 km/hr.
17)How long will it take to row 20 km upstream if one can row 10 km in 10 minutes in still water and the same distance in 8 minutes with the stream?
A. 12 min B. 13.33 min C. 24 min D. 26.67 min
Sol : Option D
Let x be the speed of man in still water and y be the speed of stream.
∴ Speed of man (x) = 60 km/hr and speed of downstream = 75 km/hr. ∴ Speed of stream = 15 km/hr.
Hence upstream speed = 60 – 15 = 45 km/hr.
So time taken to cover 20 km = 20/45*60 = 26.67min.
18)A boat makes a return journey from point A to point B and back in 5 hours 36 minutes. One way it travels with the stream and on the return it travels against the stream. If the speed of the stream increases by 2 km/hr, the return journey takes 9 hours 20 minutes. What is the speed of the boat in still water? (The distance between A and B is 16 km.)
A. 5 km/hr B. 3 km/hr C. 7 km/hr D. 9 km/hr
Sol : Option C
Let x be speed of u / s and y be the speed of d / s.
∴ (16/x) + (16/y) = (28/5) and 16/(y+2) + 16/(x-2) = 28/3
Solving these 2 equations, we get x = 4km/hr and y = 10km/hr
∴ speed of boat in still water = (4+10) / 2 = 7km/hr.
19) A boat travels from point A to B, a distance of 12 km. From A it travels 4 km downstream in 15 minutes and the remaining 8 km upstream to reach B. If the downstream speed is twice as high as the upstream speed, what is the average speed of the boat for the journey from A to B?
A. 10(2/3)km/hr B. 9.6 km/hr C. 11.16 km/hr D. 10.44 km/hr
Sol : Option B
4 km downstream is covered in 15 min. ∴ speed of downstream = 16 km/hr. So speed of upstream = 8km/hr. Total time taken for downstream journey = 15 min (given). Now total time taken for upstream journey = 8/8 = 1 hr = 60 min. Hence total time taken from A to B = 15 + 60 = 75 min. As average speed = Total distance /total time, so average speed from A to B = (12/75)*60 = 48/5 = 9.6kmph.
20) A man rows 24 km upstream in 6 hours and a distance of 35 km downstream in 7 hours. Then the speed of the man in still water is
A. 4.5 km/hr B. 4 km/hr C. 5 km/hr D. 5.5 km/hr
Sol : Option A
Speed of upstream = 24 / 6 = 4 km / hr. Speed of downstream = 35 / 7 = 5km / hr.
∴ Speed of man in still water = (4 + 5) / 2 = 4.5 km / hr.
21)A boat goes 12 km upstream in 48 minutes. The speed of stream is 2 km/hr. The speed of boat in still water is
A. 15 km/hr B. 16 km/hr C. 17 km/hr D. 18 km/hr
Sol : Option C
12 km upstream in 48 min. ⇒ it will cover 15 km in 1 hr. Speed of stream = 2 km / hr.
∴ Speed of boat in still water = 15 + 2 = 17 km / hr.
22) A motorboat can travel at 5 km/hr in still water. It travelled 90 km downstream in a river and then returned, taking altogether 100 hours. Find the rate of flow of the river.
A. 3 km/hr B. 3.5 km/hr C. 2 km/hr D. 4 km/hr
Sol : Option D
Speed of boat in still water = x = 5 km/hr.
Let rate of flow of river = y km/hr. ∴ Speed of u/s = 5- y and speed of d / s = 5 + y
∴ 90/(5+y) + 90/(5-y) = 100 ⇒ y = 4 km/hr.
23)A boatman can row 2 km against the stream in 20 minutes and return in 10 minutes. Find the rate of flow of the current.
A. 2 km/h B. 1 km/h C. 3 km/h D. 5 km/h
Sol : Option C
Let x be the speed of man in still water and y be the speed of current.
Speed of d / s = (2 / 10) × 60 = 12 km / hr. Speed of u / s = (2 / 20) × 60 = 6 km / hr.
∴ rate of current = (12 - 6) / 2 = 3 km/hr.
24) A man can row 30 km upstream in 6 hours. If the speed of the man in still water is 6 km/hr, find how much he can row downstream in 10 hours.
A. 70 km B. 140 km C. 200 km D. 250 km
Sol : Option A
Speed of upstream = 30 / 6 = 5 km / hr. Speed of man in still water = 6 km / hr.
∴ Speed of current = 6 - 5 = 1 km / hr. So speed of downstream = 6 + 1 = 7 km / hr.
∴ Distance traveled in 7 hrs = 10 * 7 = 70 km.
25) A boat running downstream covers a distance of 16km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?
a)4km/hr
b)6km/hr
c)8km/hr
d) None of these
Rate of downstream=(16/2 ) kmph=8kmph
Rate of upstream =(16/4) kmph=4kmph
Therefore Speed in still water=1/2(8+4) kmph=6kmph
26)A man can row a boat 27km/h with the stream and 11km/h against the stream.
Find speed of stream
a) 2km/hr
b)4km/hr
c)8km/hr
d)10km/hr
Solution: Speed (Rate) of stream = ½ (u-v) km/hr = ½ (27-11)=8km/hr
27) A man can row a boat 12 km/h with the stream and 8km/h against the stream.
Find his speed in still water.
a) 2km/hr
b) 4km/hr
c) 8km/hr
d) 10km/hr
Solution: Speed of boat in still water = ½(u+v) km/hr = ½ (12+8)=10km/hr
28) A man rows downstream 32 km and 14km upstream. If he takes 6 hours to cover each distance, then the velocity (in kmph) of the current is:
a)1/2
b)1
c)1and ½
d)2
Solution: Rate downstream=(32/6)kmph; Rate upstream=(14/6)kmph
Velocity of current=1/2(32/6 - 14/6)kmph=3/2kmph=1.5kmph
29) In one hour, a boat goes 11km along the stream and 5km against the stream.
The speed of the boat in still water (in km/hr)is:
a)3
b)5
c)8
d)9
Solution: Speed in still water=1/2(11+5)kmph=8kmph
30) Speed of a boat in still water is 16km/h. If it can travel 20km downstream in the same time as it can travel 12 km upstream, the rate of stream is.
a)1km/h
b)2km/h
c)4km/h
d)5km/h
Solution: Speed downstream: Speed upstream=20:12=5:3
Speed of current=5-3/5+3*16=4km/h
31)A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:
A. 9 km/hr B. 12.5 km/hr
C. 8.5 km/hr D. 10 km/hr.
Answer: Option D
Explanation:
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
32) Speed of a boat in standing water is 14 kmph and the speed of the stream is 1.2 kmph. A man rows to a place at a distance of 4864 km and comes back to the starting point. The total time taken by him is:
A. 1400 hours B. 350 hours
C. 700 hours D. 1010 hours
Answer: Option C
Explanation:
Speed downstream = (14 + 1.2) = 15.2 kmph
Speed upstream = (14 - 1.2) = 12.8 kmph
4864 4864
Total time taken = ____ + ____
15.2 12.8
= 320 + 380
= 700 hours
33)The speed of a boat in still water in 22 km/hr and the rate of current is 4 km/hr. The distance travelled downstream in 24 minutes is:
A. 10.4 km B. 9.4 km
C. 10.2 km D. 9.2 km
Answer: Option A
Explanation:
Speed downstream = (22 + 4) = 26 kmph
Time = 24 minutes = 24/60 hour = 2/5 hour
Distance travelled = Time × speed
= (2/5)*26
= 10.4 km
34)A boat covers a certain distance downstream in 1 hour, while it comes back in 11⁄2 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?
A. 15 kmph B. 12 kmph
C. 13 kmph D. 14 kmph
Answer: Option A
Explanation:
Let the speed of the water in still water
=x
Given that speed of the stream = 3 kmph
Speed downstream = (x+3)kmph
Speed upstream = (x-3)kmph
He travels a certain distance downstream in 1 hour and come back in 11⁄2 hour.
i.e., distance travelled downstream in 1 hour = distance travelled upstream in 1 1⁄2 hour
Since distance = speed × time, we have
(x+3) * 1 = (x-3) 3/2
=>2(x+3) = 3(x-3)
=>2x+6 = 3x-9
=>x= 6+9 = 15kmph
35)A boat can travel with a speed of 22 km/hr in still water. If the speed of the stream is 5 km/hr, find the time taken by the boat to go 54 km downstream
A. 3 hours B. 2 hours
C. 4 hours D. 5 hours
Answer: Option B
Explanation:
Speed of the boat in still water = 22 km/hr
speed of the stream = 5 km/hr
Speed downstream = (22+5) = 27 km/hr
Distance travelled downstream = 54 km
Time taken = distance / speed
=54/27
= 2 hours
36) A boat running downstream covers a distance of 22 km in 4 hours while for covering the same distance upstream, it takes 5 hours. What is the speed of the boat in still water?
A. 4.95 kmph B. 5 kmph
C. 4.75 kmph D. 4.65
Answer: Option A
Explanation:
Speed downstream = 22/4 = 5.5kmph
speed upstream = 22/5 = 4.4 kmph
speed of the boat in still water = (5.5 = 4.4) / 2 = 4.95 kmph
37) A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is:
A. 2 : 1 B. 3 : 1
C. 1 : 2 D. 1 : 3
Answer: Option B
Explanation:
Let speed upstream = x
Then, speed downstream = 2x
Speed in still water = (2x +x)/2 = 3x/2
speed of the stream = (2x -x)/2 = x/2
speed in still water : speed of the stream
= 3x/2 : x/2
= 3:1
38)A man can row at 5 kmph in still water. If the velocity of current is 1 kmph and it takes him 1 hour to row to a place and come back, how far is the place?
A. 3.6 km B. 2.4 km
C. 3.2 km D. 3 km
Answer: Option B
Explanation:
Speed in still water = 5 kmph
Speed of the current = 1 kmph
Speed downstream = (5 +1) = 6kmph
Speed upstream = (5-1) = 4kmph
Let the required distance be x km
Total time taken = 1 hour
=>x/6 + x/4 =1
=> 2x + 3x =12
=>5x=12
=> x= 2.4km
39)A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
A. 4 mph B. 2 mph
C. 2.5 mph D. 3 mph
Answer: Option B
Explanation:
Speed of the boat in still water = 10 mph
Let speed of the stream be x mph
Then, speed downstream = (10+x)mph
speed upstream = (10-x) mph
Time taken to travel 36 miles upstream - Time taken to travel 36 miles downstream= 90/60 hours
=> [36 / (10-x)] - [36 / (10+x)] = 3/2
=> [12 / (10 -x)]- [12 / (10+x)] = 1/2
=> 24(10 +x) - 24(10-x) = (10+x)(10-x)
=>240 + 24x -240 +24x = (100-x^2)
=>48x = 100=x^2
=>x^2 +48x-100 = 0
=> (x+50)(x-2) = 0
=>x= -50 or 2
Since x can not be negative, x = 2 mph
40)A boat covers a certain distance downstream in 4 hours but takes 6 hours to return upstream to the starting point. If the speed of the stream be 3 km/hr, find the speed of the boat in still water
A. 12 km/hr B. 13 km/hr
C. 14 km/hr D. 15 km/hr
Answer: Option D
Explanation:
Let the speed of the water in still water = x
Given that speed of the stream = 3kmph
Speed downstream = (x+3) kmph
speed upstream = (x-3)kmph
He travels a certain distance downstream in 4 hour and come back in 6 hour.
ie, distance travelled downstream in 4 hour = distance travelled upstream in 6 hour
since distance = speed × time, we have
(x+3)*4 = (x-3)*6
=>(x+3)2 = (x-3)3
=>2x +6 = 3x -9
=>x = 6+9 = 15kmph
41)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:
A. 5 kmph B. 12 kmph
C. 7 kmph D. 8 kmph
Answer: Option C
Explanation:
Let the rate along with the current is x km/hr
(x+3) /2 =5
=>x+3 = 10
=>x= 7kmph
42)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 ?
A) 180 km B) 160 km
C) 140 km D) 120 km
Answer & ExplanationAnswer: A) 180 km
Explanation:
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
43)A boat sails 15 km of a river towards upstream in 5 hours. How long will it take to cover the same distance downstream, if the speed of current is one-fourth the speed of the boat in still water:
A) 1.8h B) 3h
C) 4h D) 5h
Answer & ExplanationAnswer: B) 3h
Explanation:
Upstream speed = B-S
Downstream speed = B+s
B-S = 15/5 = 3 km/h
Again B= 4S
Therefore B-S = 3= 3S
=> S = 1 and B= 4 km/h
Therefore B+S = 5km/h
Therefore, Time during downstream = 15/5 = 3h
44)The current of a stream at 1 kmph. A motor boat goes 35 km upstream and back to the starting point in 12 hours. The speed of the motor boat in still water is ?
A) 8 kmph B) 6 kmph
C) 7.5 kmph D) 5.5 kmph
Answer & ExplanationAnswer: B) 6 kmph
Explanation:
Speed of the stream = 1
Motor boat speed in still water be = x kmph
Down Stream = x + 1 kmph
Up Stream = x - 1 kmph
[35/(x + 1)] + [35/(x - 1)] = 12
x = 6 kmph
45)A man can row 6 kmph in still water. When the river is running at 1.2 kmph, it takes him 1 hour to row to a place and back. What is the total distance traveled by the man ?
A) 4.58 kms B) 6.35 kms
C) 5.76 kms D) 5.24 kms
Answer & ExplanationAnswer: C) 5.76 kms
Explanation:
Speed in still water = 6 kmph
Stream speed = 1.2 kmph
Down stream = 7.2 kmph
Up Stream = 4.8 kmph
x/7.2 + x/4.8 = 1
x = 2.88
Total Distance = 2.88 x 2 = 5.76 kms
46)A boy can swim in still water at 4.5 km/h, but takes twice as long to swim upstream than downstream. The speed of the stream is ?
A) 1.8 kmph B) 2 kmph
C) 2.2 kmph D) 1.5 kmph
Answer & ExplanationAnswer: D) 1.5 kmph
Explanation:
Speed of Boy is B = 4.5 kmph
Let the speed of the stream is S = x kmph
Then speed in Down Stream = 4.5 + x
speed in Up Stream = 4.5 - x
As the distance is same,
=> 4.5 + x = (4.5 - x)2
=> 4.5 + x = 9 -2x
3x = 4.5
x = 1.5 kmph
47)A boatman can row 3 km against the stream in 20 minutes and return in 18 minutes. Find the rate of current ?
A) 1/3 kmph B) 2/3 kmph
C) 1/4 kmph D) 1/2 kmph
Answer & ExplanationAnswer: D) 1/2 kmph
Explanation:
Speed in upstream = Distance / Time = 3 x 60/20 = 9 km/hr.
Speed in downstream = 3 x 60/18 = 10 km/hr
Rate of current = (10-9)/2 = 1/2 km/hr.
48)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 ?
A) 1.5 hrs B) 1 hrs
C) 2.5 hrs D) 2 hrs
Answer & ExplanationAnswer: D) 2 hrs
Explanation:
Speed in downstream = 96/8 = 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 = 8/4 = 2 hours.
49)A man rows his boat 60 km downstream and 30 km upstream taking 3 hrs each time. Find the speed of the stream ?
A) 5 kmph B) 10 kmph
C) 15 kmph D) 45 kmph
Answer & ExplanationAnswer: A) 5 kmph
Explanation:
Speed of the boat downstream s=a/t= 60/3 = 20 kmph
Speed of the boat upstream s= d/t = 30/3= 10 kmph
Therefore, The speed of the stream = (speed of downstream − speed of upstream) / 2 = 5 kmph
50)A man goes down stream with a boat to some destination and returns upstream to his original place in 5 hours. If the speed of the boat in still water and the strean are 10km/hr and 14km/hr respectively, the distance of the destination from the string place is
A) 16 km B) 18 km
C) 21 km D) 25 km
Answer & ExplanationAnswer: C) 21 km
Explanation:
Let the distance covered be D km.
D / (10+4) + D / (10−4) = 5
D / 14+D / 6=5
10D = 42 x 5 = 210
=> D = 21 km
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