BOATS AND STREAMS EXAMPLE QUESTIONS PART 2
51)A man swims downstream 72 km and upstream 45 km taking 9 hours each time; what is the speed of the current ?
A) 1 kmph B) 3.2 kmph
C) 1.5 kmph D) 2 kmph
Answer & ExplanationAnswer: C) 1.5 kmph
Explanation:
72 --- 9
? ---- 1
=> Down Stream = 8
45 ---- 9
? ---- 1
=> Up Stream = 5
Speed of current S = ?
S = (8 - 5)/2 = 1.5 kmph.
52)A man can row 8 kmh in still water. If the river is running at 2 kmh, it takes 4 hrs more upstream than to go downstream for the same distance. Then the distance is given by
A) 54 kms B) 32 kms
C) 45 kms D) 60 kms
Answer & ExplanationAnswer: D) 60 kms
Explanation:
Let the distance be d.
d / (8−2) − d / (8+2) = 4
=> 2d = 120
=> d = 60 kms.
53)In one hour, a boat goes 12 km/hr along the stream and 6 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
A) 9 B) 8
C) 7 D) 7.5
Answer & ExplanationAnswer: A) 9
Explanation:
Speed in still water = Average of Speed in Upstream and speed in Downstream
= 1/2 (12 + 6) kmph = 9 kmph.
54)A boat travels 72 km downstream in 8 hours and 84 km upstream in 12 hours. Find the speed of the boat in still water and the speed of the water current ?
A) 9 and 3 kmph B) 6 and 7 kmph
C) 8 and 1 kmph D) 7 and 2 kmph
Answer & ExplanationAnswer: C) 8 and 1 kmph
Explanation:
Downstream speed = 72km/8hrs = 9 kmph
upstream speed = 84km/12hrs = 7 kmph
speed of boat = avg of downstream and upstream speeds
speed of boat = (9+7)/2kmph = 8 kmph.
current speed = half of the difference of downstream and upstream speeds
currend speed = (9-7)/2kmph = 1 kmph
55)A boat whose speed in still water is 9 kmph, goes 12 km downstream and comes back in 3 hrs. Find the speed of the stream?
A) 1 kmph B) 3 kmph
C) 5 kmph D) 4 kmph
Answer & ExplanationAnswer: B) 3 kmph
Explanation:
Let the speed of the stream = x kmph
From the given data,
12 /(9+x) + 12 / (9−x)=3 hrs
3 x^2 = 27
=> x = 3 kmph
Therefore, the speed of the stream = 3 kmph
56)A person can row 8 1/2 km an hour in still water and he finds that it takes him twice as long to row up as to row down the river. The speed of the stream ?
A) 1.78 kmph B) 2.35 kmph
C) 2.83 kmph D) 3.15 kmph
Answer & ExplanationAnswer: C) 2.83 kmph
Explanation:
Given speed of the person = 8 1/2 = 17/2 kmph
Let the speed of the stream = x kmph
speed of upstream = 17/2 - x
speed of downstream = 17/2 + x
But given that,
2(17/2 - x) = 17/2 + x
=> 3x = 17/2
=> x = 2.83 kmph.
57)If sum of upstream and downstream speed of a boat is 82 kmph, and the boat travels 105 km. upstream in 3 hr, Find the time taken by boat to cover 126 km downstream.
A) 2.8 hrs B) 2.7 hrs
C) 2.6 hrs D) 2.5 hrs
Answer & ExplanationAnswer: B) 2.7 hrs
Explanation:
Let Speed of boat in still water = b
Let Speed of still water = w
Then we know that,
Speed of Upstream = U = boat - water
Speed of Downstream = D = boat + water
Given, U + D = 82
b - w + b + w = 82
2b = 82
=> b = 41 kmph
From the given data,
41 - w = 105/3 = 35
w = 6 kmph
Now,
b + w = 126/t
=> 41 + 6 = 126/t
=> t = 126/47 = 2.68 hrs.
58)A motorboat goes 8 km an hour in still water, but takes thrice as much time in going the same distance against the current than going with the current. Then find the speed of the current?
A) 4 kmph B) 6 kmph
C) 3 kmph D) 2 kmph
Answer & ExplanationAnswer: A) 4 kmph
Explanation:
Let the speed of current = 'C' km/hr
Given the speed of boat in still water = 6 kmph
Let 'd' kms be the distance it covers.
According to the given data,
Boat takes thrice as much time in going the same distance against the current than going with the current
i.e, d/(8 − C) = 3 × d / (8 + C)
⇒ 24 − 3C = 8 + C⇒ 4C = 16⇒ C = 4 kmph
Hence, the speed of the current C = 4 kmph
59)A man can row against the current three fourth of a kilometer in 15 min and returns same distance in 10 min, then ratio of his speed to that of current?
A) 5:1 B) 3:1
C) 4:1 D) 2:1
Answer & ExplanationAnswer: A) 5:1
Explanation:
Let the speed of the man in still water = p kmph
Speed of the current = s kmph
Now, according to the questions
(p + s) x 10 = (p - s) x 15
2p + 2s = 3p - 3s
=> p : s = 5 : 1
Hence, ratio of his speed to that of current = 5:1.
60) A man can row upstream at 16 km/hr and downstream at 24 km/hr. Find the speed of the current.
A) 4 kmph B) 6 kmph
C) 5 kmph D) 3 kmph
Answer & ExplanationAnswer: A) 4 kmph
Explanation:
Speed of the current = 24-16/2
= 8/2
= 4 km/hr.
61)Amith can row a boat d km upstream and the same distance downstream in 5 hours 15 minutes. Also, he can row the boat 2d km upstream in 7 hours. How long will it take to row the same distance 2d km downstream for Amith ?
A) 4 hrs 10 min B) 3 hrs 15 min
C) 3 hrs 30 min D) 4 hrs 1 min
Answer & ExplanationAnswer: C) 3 hrs 30 min
Explanation:
Let the speed of boat and stream be x and y kmph respectively.
According to question
d/x+y + d/x-y = 5h 15m or 21/4 hrs ......(i)
and 2d/x-y = 7...... (ii)
From eq. (i) and (ii)
2d/x+y = 7/2
Hence, Amith will take to row 2d km distance downstream in 7/2 hrs
= 3.5 hrs
= 3 hrs 30 min.
62)A boat while travelling upstream covers a distance of 29 km at the speed of 6 km/h, whereas while travelling downstream it covers the same distance at a speed of 12 km/h. What is the speed of the boat in still water?
A) 6 kmph B) 8 kmph
C) 9 kmph D) 11 kmph
Answer & ExplanationAnswer: C) 9 kmph
Explanation:
Speed of boat in still water = 1/2 (12 + 6) = 9 kmph.
63)Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?
A) 2 kmph B) 4 kmph
C) 6 kmph D) 8 kmph
Answer & ExplanationAnswer: B) 4 kmph
Explanation:
Let the distance in one direction = k kms
Speed in still water = 4.5 kmph
Speed of river = 1.5
Hence, speed in upstream = 4.5 - 1.5 = 3 kmph
Speed in downstream = 4.5 + 1.5 = 6 kmph
Time taken by Rajesh to row upwards = k/3 hrs
Time taken by Rajesh to row downwards = k/6 hrs
Now, required Average speed =Total distance / Total speed
= 2k / (k/3 + k/6) = (2k x 18)/(6k + 3k) = 4 kmph
Therefore, the average speed of the whole journey = 4kmph.
64)A motorboat can go 10 miles downstream on a river in 20 min. It takes 30 min for this boat to go back at the same 10 miles. Find the speed of the current ?
A) 8 m/h B) 5 m/h
C) 7 m/h D) 6 m/h
Answer & ExplanationAnswer: B) 5 m/h
Explanation:
As the distance travelled is constant, the time taken is inversely proportional to speed.
Let 'u' be the speed of the current and 'v' be the speed of the boat.
Speed of the boat downstream = v + u & upstream = v - u
=> v+u/v-u = 30/20 => v/u = 5 => v = 5u
=> v + u = 6u = 10/20/60 miles/hr
=> 6u = 30 m/h
=> u = 5 m/h
65)A boat takes 2 hours to travel from point A to B in still water. To find out its speed upstream, which of the following information is/are required?
A. Distance between point A and B.
B. Time taken to travel downstream from B to A.
C. Speed of the stream of water.
A) Only A and B B) Only B and C
C) All are required D) Any one pair of A and B, B and C or C and A is sufficient
Answer & ExplanationAnswer: D) Any one pair of A and B, B and C or C and A is sufficient
Explanation:
Let distance between A & B = d km
Let speed in still water = x kmph
Let speed of current = y kmph
from the given data,
d/x = 2
From A) we get d
From B) we get d/x+y
From C) we get y
So, Any one pair of A and B, B and C or C and A is sufficient to give the answer i.e, the speed of upstream.
66) 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) 1 : 3 B) 3 : 2
C) 2 : 3 D) 3 : 1
Answer & ExplanationAnswer: A) 1 : 3
Explanation:
Let the speed of the boat in still water is 'w'
Speed of the current is 'c'
Let the distance between two places is 'd'
According to the question, motorboat takes half time to cover a certain distance downstream than upstream.
d / w+c = 1/2(d / w−c)
=> 2w - 2c = w + c
=> w = 3c
=> c : w = 1 : 3
Hence, the ratio between rate of current(c) and rate of boat in still water(w) = 1 : 3
67)A Woman’s downstream swimming rate is thrice of her upstream swimming rate. If she covers 12 km upstream in 2.5 hours, what distance she will cover in 5 hours downstream?
A) 72 km B) 36 km
C) 56 km D) 42 km
Answer & ExplanationAnswer: A) 72 km
Explanation:
Rate of her upstream = 12/2.5 = 4.8 km/hr
Then, ATQ
Rate of downstream = 4.8 x 3 = 14.4 km/hr
Hence, the distance she covers downstream in 5 hrs = 14.4 x 5 = 72 kms.
68)If the boat goes 7 kms upstream in 42 min and speed of the stream is 3 kmph, then the speed of the boat in still water ?
A) 14 kmph B) 13 kmph
C) 12 kmph D) 11 kmph
Answer & ExplanationAnswer: B) 13 kmph
Explanation:
Given that, upstream distance = 7 kms
Upstream speed = 7/42 x 60 = 10 kms
Speed of the stream = 3 kmph
Let speed in still water = M kmph, then
Upstream speed = M - 3 = 10
=> M = 13 kmph.
69)Find the speed of stream if a boat covers 36 km in downstream in 6 hours which is 3 hours less in covering the same distance in upstream?
A) 1.5 kmph B) 1 kmph
C) 0.75 kmph D) 0.5 kmph
Answer & ExplanationAnswer: B) 1 kmph
Explanation:
Speed of the boat upstream = 36/9 = 4 kmph
Speed of the boat in downstream = 36/6 = 6 kmph
Speed of stream = 6-4/2 = 1 kmph
70)Sravan drove from home to a neighboring town at the speed of 50 km/h and on his returning journey, he drove at the speed of 45 km/h and also took an hour longer to reach home. What distance did he cover?
A) 350 kms B) 450 kms
C) 900 kms D) 700 kms
Answer & ExplanationAnswer: C) 900 kms
Explanation:
Let the distance he covered each way = d kms
According to the question,
d/45 - d/50 = 1
=> d = 450 kms.
Hence, the total distance he covered in his way = d + d = 2 d = 2 x 450 = 900 kms.
71)Equal distance is covered by a boat in upstream and in downstream in total 5 hours. Sum of speed of a boat in upstream and downstream is 40 km/hr. Speed of boat in still water is 600%
more than the speed of stream. Find theapproximate distance covered by boat in downstream (in km).
A) 45 B) 50
C) 55 D) 60
Answer & ExplanationAnswer: B) 50
Explanation:
let speed of boat= X, speed of stream= Y
Upstream speed= X-Y
Downstream speed= X+Y
Sum of upstream & downstream= (X-Y) +(X+Y)= 2X
So, 2X= 40
X= 20 km/hr
Speed of boat : speed of stream= 600+100 :100= 7:1
So speed of Stream= 20/7 km/hr
ATQ, D/( X-Y) + D/( X+Y) = 5
D/(120/7) + D/(160/7)= 5
D= 480×5/49= 48.97 km= 50 Km(approx)
72)The ratio of the speed of a boat downstream and speed of the stream is 9:1. If the speed of the current is 3 km per hr, find the distance travelled by the boat upstream in 5 hours.
A) 100 km B) 98 km
C) 109 km D) 105 km
Answer & ExplanationAnswer: D) 105 km
Explanation:
Let the speed of boat in still water is ‘x’ km/hr & that of stream is ‘y’ km/hr.
Then, ATQ
(x+y)/y = 9/1 9y = x + y
x = 8y
y = 3 km/hr
So, x = 24 km/hr
Upstream speed = 24-3 = 21 km/hr
Hence, distance travelled upstream in 5 hours = 21*5 = 105 km.
73)A steamer moves with a speed of 4.5 km/h in still water to a certain upstream point and comes back to the starting point in a river which flows at 1.5 km/h. The average speed of steamer for the total journey is
A) 12 km/h B) 10 km/h
C) 6 km/h D) 4 km/h
Answer & ExplanationAnswer: D) 4 km/h
Explanation:
Speed of streamer = 4.5 km/hrSpeed of water = 1.5 km/hr
Downstream speed = 4.5+1.5 = 6 km/hr
Upstream speed = 4.5 -1.5 = 3 km/hr
Average Speed = (6 X 3) / 4.5 = 4km/hr
74)Ashok can row upstream at 8 kmph and downstream at 12kmph.What is the speed of the stream ?
A) 6 km/hr B) 3 km/hr
C) 2 km/hr D) 4.5 km/hr
Answer & ExplanationAnswer: C) 2 km/hr
Explanation:
If the speed downstream is a kmph and the speedup stream is b kmph then
Speed of the stream = 1/2 x (a–b) kmph
Speed downstream a = 12kmph
Speed upstream b = 8 kmph
Speed of the stream = 1/2 x (a–b) = 1/2 x (12–8)= 4/2 = 2 kmph
75)Choose the most appropriate answer: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 9 Km/h and the speed of the current is 3 Km/h, the distance between A and B is
A) 9 km B) 10 km
C) 11 km D) 12 km
Answer & ExplanationAnswer: D) 12 km
Explanation:
Speed of boat in still water = 9 km/hr
Speed of current = 3km/hr
Downstream speed = 9+3 = 12 km/hr
Upstream speed = 9-3 =6 km/hr
Let the distance between A to B be x km.
x/6 + x/12 = 3x + 2x = 36
3x = 36
x = 12 km
76)A boat travels 24 km upstream in 6 h and 20 km downstream in 4 h. then, the speed of a boat in still water and the speed of current are respectively
A) 4.5 km/h and 3 km/h B) 4.5 km/h and 0.5 km/h
C) 4 km/h and 2 km/h 5 km/h and 2 km/h D) 5 km/h and 2 km/h
Answer & ExplanationAnswer: B) 4.5 km/h and 0.5 km/h
Explanation:
Distance travelled by boat in upstream=24km
Time taken = 6 h
Speed of the boat in upstream = 24/6 = 4 km/h
And distance travelled by boat in downstream = 20 km
Time taken = 4h Speed of the boat in downstream = 20/4 km/h = 5 km/h
Now, speed of the boat in still water = 1/2 [ speed of the boat in upstream + speed of the boat in downstream] =1/2 [4 + 5] = 1/2 × 9 = 4.5 km/h
And speed of the current = 1⁄2 [speed of the boat in downstream – speed of the boat in upstream] = 1/2 [5 – 4] = 1/2 × 1 = 0.5 km/h
77)
Mahesh rows to the place 80 km away and back in 20 hours. He finds that he can row 8 km downstream in the same time as 4 km upstream. The speed of the boat in stillwater is
A) 9 kmph B) 7 kmph
C) 2 kmph D) 5 kmph
Answer & ExplanationAnswer: A) 9 kmph
Explanation:
If Mahesh moves 8 km downstream in X hours
Downstream speed = 8/X kmph
upstream speed = 4/X kmph
Now 80/(8/X) + 80/(4/X)=20
X=2/3
downstream Speed = 8/(2/3)= 12 kmph
upstream Speed = 4/(2/3)= 6 kmph
Rate of the stream = (12+6)/2= 9 kmph
78) The speed of the boat when traveling downstream is 32 km/hr. whereas when traveling upstream it is 28 km/hr. What is the speed of the boat in still water and the speed of the stream?
Sol) This question requires direct use of the formula mentioned earlier.
Speed of the boat in still water = ½ (32 + 28) km/hr. = 30 km/hr.
Speed of the stream = ½ (32 – 28) hm/hr. = 2 km/hr
79) A boat take 8 hours to cover a distance while traveling upstream, whereas while traveling downstream it takes 6 hours. If the speed of the current is 4 km/hr. What is the speed of the boat in still water?
Sol) Again direct use of the above formula and you are done. Here, t2 is 8 hours and t1 is 6 hours and b is 4 km/hr. Therefore,
Speed of the boat in still water = 4(8+ 6)/ (8 – 6) = 4 * 14/2 = 28 km/hr.
80) 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 water resistance, it took 1 hour 15 minutes to cover the same distance. What was the average speed during the whole journey?
Sol) In this problem we cannot directly use the formula first we need to find the upstream speed and speed in still water. This can be done as follows,
Upstream speed = distance covered in 1 hour 15 minutes / Time taken to travel 50 miles = 50/5/4 = 40 miles/hr.
Boat’s speed in still water = ½ (Upstream speed + downstream speed) = ½ (40 + 60) = 50 miles/ hr.
Now we are in stage of using the average speed formula.
Average speed during whole journey = (40 * 60)/ 50 = 48 miles/ hr.
81) Speed of boat in still water is 16 km/hr. If the speed of the stream is 4 km/hr, find its downstream and upstream speeds.
A - 15,5
B - 20,12
C - 10,6
D - 18,10
Answer - B
Explanation
Downstream Speed = u + v = 16 + 4 = 20 km/hr
Upstream Speed = u - v = 16 - 4 = 12 km/hr
82)A man can row downstream at 18 km/hr and upstream at 12 km/hr. Find his speed in still water and the rate of the current.
A - 16,3
B - 15,4
C - 15,3
D - 16,4
Answer - C
Explanation
Speed of the boat or swimmer in still water = 1/2 * (Downstream Speed + Upstream Speed)
= 1/2 * (18+12)
= 15 km/hr
Speed of the current = 1/2 * (Downstream Speed - Upstream Speed)
= 1/2 * (18-12)
= 3 km/hr
83) A man swims downstream 28 km in 4 hrs and upstream 12 km in 3 hrs. Find his speed in still water and also the speed of the current.
A - 5,2
B - 5.5,1.5
C - 5.5,2.5
D - 5,1
Answer - B
Explanation
Downstream Speed (u) = 28/4 = 7 km/hr
Upstream Speed (v) = 12/3 = 4 km/hr
Speed of the boat or swimmer in still water = 1/2*(Downstream Speed + Upstream Speed)
= 1/2*(7+4)
= 5.5 km/hr
Speed of the current = 1/2*(Downstream Speed - Upstream Speed)
= 1/2*(7-4)
= 1.5 km/hr
84) The speed of the boat in still water is 15 km/hr. It takes twice as long as to go upstream to a point as to return downstream to the starting point. What is the speed of the current?
A - 4 km/hr
B - 3 km/hr
C - 2 km/hr
D - 5 km/hr
Answer - B
Explanation
Let speed of the current = S km/hr.
As per question,
Downstream Speed = 2*Upstream speed
15 + S = 2(15 - S)
S = 3 km/hr
85) A boat covers a certain distance downstream in 6 hours and takes 8 hours to return upstream to the starting point. If the speed of the stream is 3 km/hr, find the speed of the boat in still water.
A - 1 km/hr
B - 4 km/hr
C - 3 km/hr
D - 2 km/hr
Answer - C
Explanation
t1 = 6 hrs
t2 = 8 hrs
v = 3 km/hr
u = ?
We know,
(u + v)t1 = (u - v)t2
(u + 3)6 = (u - 3)8
u = 3 km/hr
86)The speed of river Ganga is 5 km/hr. A motor boat travels 28 km upstream and then returns downstream to the starting point. If its speed in still water be 9 km/hr, find the total journey time.
A - 5 hr
B - 8 hr
C - 9 hr
D - 10 hr
Answer - C
Explanation
We know, Downstream speed = u + v = 9 + 5 = 14 km/hr
Upstream Speed = u - v = 9 - 5 = 4 km/hr
Speed = Distance/Time
∴ Time = Distance/Speed
∴ Total time taken = t1 + t2
= 28/4 + 28/14
= 7 + 2 = 9 hr
87) A boat travels 32 km upstream and 60 km downstream in 9 hr. Also it travels 40 km upstream and 84 km downstream in 12 hrs. Find the speed of the boat in still water and rate of the current.
A - 10,2
B - 8,4
C - 9,3
D - 7,5
Answer - A
Explanation
Let, upstream speed = u km/hr
Downstream speed = d km/hr
32/u + 60/d = 9 (Time = Distance/Speed)
Simlarly,
40/u + 84/d = 12
32x + 60y = 9 ...(i) (Assuming 1/u = x and 1/d = y)
40x + 84y = 12 ...(ii)
(Equation(ii) * 4) - (Equation (i)*5), we get,
y = 1/12. So, x = 1/8
Hence, downstream speed = 12 km/hr
Upstream speed = 8 km/hr
So,
Speed of the boat in still water = 1/2*(12+8) = 10 km/hr
Speed of the current = 1/2*(12 - 8) = 2 km/hr
88) The speed of a swimmer in still water is 12km/hr. It takes 6 hrs to swim to a certain distance and return to the starting point. The speed of current is 4km/hr. Find the distance between the two points.
A - 15 km
B - 16 km
C - 14 km
D - 12 km
Answer - B
Explanation
Let distance = D
Downstream time = t1; Downstream Speed = 1/2*(12+4) = 8 km/hr
Upstream Time = t2; Upstream Speed = 1/2*(12-4) = 4 km/hr
Total time = t1 + t2
6 = (D/Upstream speed) + (D/Downstream speed)
6 = D/8 + D/4
D = 16 km
89)A boat running downstream covers a distance of 30 kms in 2 hrs. While coming back the boat takes 6 hrs to cover the same distance. If the speed of the current is half that of the boat, what is the speed of the boat?
A - 15 km/hr
B - 54 km/hr
C - 10 km/hr
D - None of these
Answer - C
Explanation
Downstream Speed = 30/2 = 15 km/hr
Upstream Speed = 30/6 = 5 km/hr
Speed of the boat in still water = 1/2*(downstream speed + upstream speed)
= 1/2*(15+5)
=10km/hr
90) A steamer goes downstream from one point to the other in 4 hrs. It covers the same distance upstream in 5 hrs. If the speed of the stream is 2 km/hr, the distance between the two pints is
A - 50 km
B - 60 km
C - 70 km
D - 80 km
Answer - D
Explanation
Let the distance be D km.
∴ Downstream Speed = D/4 km/hr
And Upstream Speed = D/5 km/hr
Given, Speed of current = 2 km/hr
Speed of the current = 1/2*(Downstream Speed - Upstream Speed)
2 = 1/2*(D/4 - D/5)
D = 80 km
91) A boat goes 24km downstream in 10 hours. It takes 2 hours more to cover the same separation against the stream. What is the rate of the watercraft in still water?
A - 2.2 km/hr
B - 2.8 km/hr
C - 4 km/hr
D - 4.2 km/hr.
Answer : A
Explanation
Speed downstream=24/10 km/hr =2.4km/hr
Speed upstream =24/12 km/hr =2km/hr
Speed of the boat in still water=1/2(2.4+2) km/hr=2.2 km/hr.
92)A man columns 30 km downstream and 18 km upstream, taking 5 hours every time. Every time what is the speed of the current?
A - 1.2 km/hr
B - 1 km/hr
C - 2 km/hr
D - 1.5 km/hr
Answer : A
Explanation
Speed downstream = 30/5 km/hr =6km/hr
Speed upstream = 18/5 km/hr = 3.6km/hr
Speed of the current = 1/2 (6-3.6) km/hr = 2.4/2 km/hr = 1.2 km/hr
93)A boat running downstream covers a separation of 10km in 2 hours .While returning upstream the boat takes 5 hours to cover the same separation. In the event that the velocity of the current and flow is 1.5 kmph, what is the speed of the boat in still water?
A - 2.5 km/hr
B - 3.5 km/hr
C - 4.5 km/hr
D - 4.2 km/hr.
Answer : B
Explanation
Speed downstream =10/2 km/hr=5km/hr.
Speed upstream =10/5 km/hr = 2km/hr.
Speed of boat in still water = 1/2 (5+2)km/hr=3.5km/hr.
94) A boat can push 1 km with stream in 10 minutes and 1 km against stream in 20 minutes. What is the rate of the vessel in still Water?
A - 1.5 km/hr
B - 3 km/hr
C - 3.4 km/hr
D - 4.5 km/hr.
Answer : D
Explanation
Distance moved downstream in 10min=1km.
Distance moved downstream in 60 min= (1/10*60) km=6 km.
Distance moved upstream in 20 min =1km.
Distance moved upstream in 60 min = (1/20*60) km = 3 km.
Speed downstream =6 km/hr, Speed upstream =3 km/hr
Speed of the boat in still water =1/2(6+3) km/hr =4.5 km/hr
95) A boat running upstream takes 8 hours 48min to cover a certain separation, while it takes 4 hour to cover the same separation running downstream. What is the proportion between the velocity of the vessel and the velocity of water flow respectively?
A - 2:1
B - 3:1
C - 8:3
D - None of these
Answer : C
Explanation
Let the speed of boat be x km /hr and speed of stream be y km/hr.
44/5 * (x-y) = 4 * (x+y)
=> 44(x-y) =20 (x+y)
=> 11 (x-y) = 5(x+y)
=> 6x=16y
=> x/y= 16/6 = 8/3
=> x: y = 8:3
96) A vessel goes 6 km in an hour in still water. It requires thrice as much investment in covering the same separation against the current. Velocity of the current is:
A - 2 km/hr
B - 3 km/hr
C - 4 km/hr
D - 5 km/hr.
Answer : C
Explanation
Speed in still water =6 km/hr.
Speed against the current =6/3 km/hr =2 km/hr
Let the speed of the current be xkm/hr
6-x = 2 => x = 4 km/hr
97) A man can push seventy five percent of a kilometer against the stream in 45/4min. what's more, return in 15/2min. The velocity of the man in still water is:
A - 2 km/hr
B - 3 km/hr
C - 4 km/hr
D - 5 km/hr
Answer : D
Explanation
Distance covered upstream in 45/4 min =3/4 km.
Distance covered upstream in 1 hr = (3/4*4/45*60) km/hr = 4 km /hr.
Distance covered upstream in 15/2 min = 3/4 km.
Distance covered upstream in 1 hr = (3/4*2/15*60) km/hr = 6 km/hr
Speed of the man in still water = 1/2 (6 +4) km/hr = 5 km/h
98) The current of a stream keeps running at 4km 60 minutes. A boat goes 6 km and back to the beginning stage in 2hour. The rate of the boat in still water is:
A - 6 km/hr
B - 7.5 km/hr
C - 8 km/hr
D - 6.8 km/hr
Answer : C
Explanation
Let the speed in still water be x km/hr. Then,
Speed downstream = (x+ 4) km/hr, speed upstream = (x-4) km/hr.
6/(x+4) + 6 /(x-4) = 2
=> 1/(x+4) +1/(x-4)=2/6 =1/3
=>(x+4)+(x-4)/x^2-16=1/3
=>x^2-16=6x
=>x^2 -6x-16=0
=> (x-8) (x+2) = 0 => x = 8
99)If a man's rate with the current is 15 km/hr and the rate of the current is 11⁄2 km/hr, then his rate against the current is
A. 12.5 km/hr B. 10 km/hr
C. 12 km/hr D. 10.5 km/hr
Answer: Option C
Explanation:
Speed downstream = 15 km/hr
Rate of the current= 1 1⁄2 km/hr
Speed in still water = 15 - 1 1⁄2 = 13 1⁄2 km/hr
Rate against the current = 13 1⁄2 km/hr - 1 1⁄2 = 12 km/hr
100) The speed of the boat in still water in 12 kmph. It can travel downstream through 45 kms in 3 hrs. In what time would it cover the same distance upstream?
A. 4 hours B. 8 hours
C. 6 hours D. 5 hours
Answer: Option D
Explanation:
Speed of the boat in still water = 12 km/hr
Speed downstream = 45/3 = 15 km/hr
Speed of the stream = 15-12 = 3 km/hr
Speed upstream = 12-3 = 9 km/hr
Time taken to cover 45 km upstream =45/9
= 5 hours
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