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- Question
- A boat goes 12 km in 1 h in still water. It takes thrice time in covering the same distance against the current. Find the speed of the current.?
Options- A. 8 km/h
- B. 12 km/h
- C. 6 km/h
- D. 7 km/h
- Correct Answer
- 8 km/h
ExplanationSpeed of a boat in still water = distance / time = 12/1 = 12 km/h
Speed against the current = 12/3 km/h
Let the speed of the current = x km/h
According to the question,
12 - x = 4
? x = 8 km/h - 1. Ashutosh can row 24 km/h in still water. It takes him twice as long to row up as to row down the river. Find the rate of stream.?
Options- A. 4 km/h
- B. 18 km/h
- C. 8 km/h
- D. 15 km/h Discuss
- 2. A man can row at 10 km/h in still water. If he takes total 5 h to go to a place 24 km away and return, then the speed of the water current is?
Options- A. 2 km/h
- B. 3 km/h
- C. 1/2 km/h
- D. 1 km/h Discuss
- 3. A boat cover a distance of 30 km downstream in 2 h while it takes 6 h to cover the same distance distance upstream. What is the speed of the boat (in km/h)?
Options- A. 5
- B. 7.5
- C. 13
- D. 10 Discuss
- 4. The speed of the current is 5 km/h. A motorboat goes 10 km upstream and back again to the starting point in 50 min. The speed, (in km/h) of the motorboat in still water is?
Options- A. 20 km/h
- B. 26 km/h
- C. 25 km/h
- D. 28 km/h Discuss
- 5. A man can row 6 km/h in still water. If the speed of the current is 2 km/h, it takes 3 h more in upstream than in the downstream for the same distance. The distance is?
Options- A. 30 km
- B. 24 km
- C. 20 km
- D. 32 km Discuss
- 6. A boatman takes twice as long to row a distance against the stream as to row the same distance with the stream. Find the ratio of speeds of the boat in still water and the stream.?
Options- A. 2 : 1
- B. 3 : 1
- C. 1 : 2
- D. 1 : 3 Discuss
- 7. A river is flowing with a steady speed of 4 km/h. One rows his boat downstream in the river and then returns by rowing upstream in the same river. When he returns to the starting points, the total distance covered by him is 42 km. If the return journey takes 2 h more than his outward journey, then the speed of his rowing in still water must be?
Options- A. 12 km/h
- B. 10 km/h
- C. 9 km/h
- D. 8 km/h Discuss
- 8. A river is flowing at a speed of 5 km/h in a particular direction. A man, who can swim at a speed of 20 km/h in still water, starts swimming along the direction of flow of the river from from points A and reaches another point B which is at a distance of 30 km from the starting point A. On reaching point B, the man turns back and starts swimming against the direction of flow of the river and stops after reaching point A. The total time taken by the man to complete his journey is?
Options- A. 2 h 30 min
- B. 3 h 12 min
- C. 3 h 30 min
- D. 3 h 45 min Discuss
- 9. Ishwar is rowing a boat. He takes half time in moving a certain distance downstream than upstream. What is the ratio of the rate of boat in still water to the rate of current?
Options- A. 2 : 1
- B. 5 : 1
- C. 7 : 1
- D. 3 : 1 Discuss
- 10. A man can row 7 1/ 2 km/h in still water. If in a river running at 1.5 km/h, it takes him 50 min to row to a place and back, how far off is the place?
Options- A. 3 km
- B. 4 km
- C. 1 km
- D. 2 km Discuss
Boats and Streams problems
Search Results
Correct Answer: 8 km/h
Explanation:
Let rate of stream be 'a' km/h.
According to the question.
24 + a = 2(24 - a)
? 24 + a = 48 - 2a
? 3a = 48 - 24 = 24
? a = 24/3 = 8 km/h
Correct Answer: 2 km/h
Explanation:
Let speed of water current be x km/h
? Speed downstream = (10 + x) km/h.
Speed upstream = (10 - x) km/h
According to the question,
24/(10 + x) + 24/(10 - x) = 5
? 24[10 - x + 10 + x] = 5(102 - x2)
? 100 - x2 = (24 x 20) / 5
? 100 - x2 = 96
? x2 = 4
? x = ?4 = 2km/h
Correct Answer: 10
Explanation:
Speed of boat downstream = Distance covered / Time taken
= 30/2 = 15 km/h
Now, speed of boat upstream = Distance covered / Time taken
= 30/6 = 5 km/h
Now, speed of boat = (Speed download + Speed upstream) / 2
= (15 + 5) / 2 = 10 km/h
Correct Answer: 25 km/h
Explanation:
Let speed of boat be x km/h.
Given speed of current = 5 km/h
? Upstream speed of boat = (x -5) km/h
Downstream speed of boat = (x + 5) km/h
According to the question.
10/(x - 5) + 10/(x + 5) = 50/60
? 10(x + 5 + x - 5)/( x2 - 25) = 5/6
? x2 -24x - 25 = 0
? x2 - 25x + x - 25 = 0
? (x - 25) (x + 1) = 0
? x = 25 [? x ? -1]
Correct Answer: 24 km
Explanation:
Let total distance be x km.
According to the question,
x/(6 + 2) + 3 = x/6 - 2
? x/8 + 3 = x/4
? x/4 - x/8 = 3
? 2x - x/8 = 3
? x = 8 x 3 = 24 km
Correct Answer: 3 : 1
Explanation:
Let boatman's speed upstream x
And his speed downstream = 2x
? Ratio = (Speed in still water) : (Speed of stream)
= (2x + x/2) : (2x - x/2)
= 3x/2 : x/2
= 3 : 1
Correct Answer: 10 km/h
Explanation:
Let the speed of rowing in still water be u km/h.
Distance in downstream motion = 21 km
and speed downstream = (u + 4) km/h
? Time taken = 21/ (u + 4)
Distance upstream motion = 21 km and speed upstream = (u +4) km
? Time taken = 21/(u - 4)
According to the question.
21/(u + 4) + 2 = 21/(u - 4)
? (21 + 2u + 8)/u + 4 = 21/(u - 4)
? (2u + 29)/(u + 4) = 21/(u - 4)
? (u - 4) (2u + 29) = 21(u + 4)
? 2u2 - 8u + 29u - 116 = 21u + 84
? 2u2 + 21u - 116 = 21u + 84
? 2u2 = 84 + 116
? u2 = 200/2
? u2 = 100
? u = 10 km/h
Correct Answer: 3 h 12 min
Explanation:
Given,
Speed of the stream = 5 km/h
and speed of the man in still water = 20 km/h
? Speed of the man downstream = 20 + 5 = 25 km/h
and speed of the man upstream = 20 - 5 = 15 km/h
? Total time taken to complete the whole journey = 30/25 + 30/15
= (30 x 8) / 75
= 3 h 12 min
Correct Answer: 3 : 1
Explanation:
Let speed of Ishwar's boat in still water be x km/h
and speed of current = y km/h
Rate downstream = (x + y) km/h
Rate upstream = (x - y) km/h
Let the distance covered in each case be a.
According to the question,
2a/(x + y) = a/(x - y)
? 2(x - y) = x + y
2x - 2y = x + y
? x = 3y
? x/y = 3/1
? x : y = 3 : 1
Correct Answer: 3 km
Explanation:
Let the distance be L km.
Speed of the main in still water = 71/2 km/h
and speed of the river = 15 km/h
? Speed of the man downstream = 7.5 + 1.5 = 9
Speed of the man upstream = 7.5 - 1.5 = 6 km/h
According to the question,
L/9 + L/6 = 50/60
? (4L + 6L)/36 = 50/60
? 10L/36 = 50/60
? L = (50 x 36)/(10 x 60)
5? x = 3 km
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