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- Question
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.
Options- A. 2.8 hrs
- B. 2.7 hrs
- C. 2.6 hrs
- D. 2.5 hrs
- Correct Answer
- 2.7 hrs
ExplanationLet 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.
- 1. 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:
Options- A. 9
- B. 8
- C. 7
- D. 7.5 Discuss
- 2. 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 ?
Options- A. 8 m/h
- B. 5 m/h
- C. 7 m/h
- D. 6 m/h Discuss
- 3. 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
Options- A. 54 kms
- B. 32 kms
- C. 45 kms
- D. 60 kms Discuss
- 4. 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?
Options- A. 1 kmph
- B. 3 kmph
- C. 5 kmph
- D. 4 kmph Discuss
- 5. 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?
Options- A. 7:4
- B. 11:4
- C. 4:7
- D. 8:3 Discuss
- 6. 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 ?
Options- A. 9 and 3 kmph
- B. 6 and 7 kmph
- C. 8 and 1 kmph
- D. 7 and 2 kmph Discuss
- 7. 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 ?
Options- A. 1.5 hrs
- B. 1 hrs
- C. 2.5 hrs
- D. 2 hrs Discuss
- 8. 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?
Options- A. 2 kmph
- B. 4 kmph
- C. 6 kmph
- D. 8 kmph Discuss
- 9. 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?
Options- A. 1.5 kmph
- B. 1 kmph
- C. 0.75 kmph
- D. 0.5 kmph Discuss
- 10. 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?
Options- A. 5:1
- B. 3:1
- C. 4:1
- D. 2:1 Discuss
Boats and Streams problems
Search Results
Correct Answer: 9
Explanation:
Speed in still water = Average of Speed in Upstream and speed in Downstream
= 1/2 (12 + 6) kmph = 9 kmph.
Correct Answer: 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
Correct Answer: 60 kms
Explanation:
Let the distance be d.
=> 2d = 120
=> d = 60 kms.
Correct Answer: 3 kmph
Explanation:
Let the speed of the stream = x kmph
From the given data,
=> x = 3 kmph
Therefore, the speed of the stream = 3 kmph
Correct Answer: 8:3
Explanation:
Let the speed of the boat upstream be p kmph and that of downstream be q kmph
Time for upstream = 8 hrs 48 min = hrs
Time for downstream = 4 hrs
Distance in both the cases is same.
=> p x = q x 4
=> 44p/5 = 4q
=> q = 11p/5
Now, the required ratio of Speed of boat : Speed of water current
=
=> (11p/5 + p)/2 : (11p/5 - p)/2
=> 8 : 3
Correct Answer: 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
Correct Answer: 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.
Correct Answer: 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 =
Therefore, the average speed of the whole journey = 4kmph.
Correct Answer: 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
Correct Answer: 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.
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