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- Question
- 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
- Correct Answer
- 10
ExplanationSpeed 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 - 1. 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
- 2. 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
- 3. Pawan can row 24 km/h in still water. When the river is running at 4.8 km/h, it takes him 1 h to row to a place and to come back. How far is the place?
Options- A. 11.52 km
- B. 14 km
- C. 12.52 km
- D. 15 km Discuss
- 4. Sameer can row a certain distance downstream in 24 h and can come back covering the same distance in 36 h. If the stream flows at the rate of 12 km/h, find the speed of Sameer in still water?
Options- A. 30 km/h
- B. 15 km/h
- C. 40 km/h
- D. 60 km/h Discuss
- 5. A sailor sails a distance of 48 km along the flow of a river in 8 h. If it takes 12 h to return the same distance, then the speed of the flow of the river is?
Options- A. 0.5 km/h
- B. 1 km/h
- C. 1.5 km/h
- D. 2 km/h Discuss
- 6. 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
- 7. 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
- 8. 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 Discuss
- 9. 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
- 10. 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
Boats and Streams problems
Search Results
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: 11.52 km
Explanation:
Pawan's speed downstream = 24 + 4.8 = 28.8 km/h
Pawan's speed upstream = 24 - 4.8 = 19.2 km/h
Let the required distance be x.
According to the question.
x/28.8 + x/19.2 = 1
? (19.2x + 28.8x) / 552.96 = 1
? 19.2x + 28.8x = 552.96
? 48x = 552.96
? x = 552.96/48 = 11.52 km
Correct Answer: 60 km/h
Explanation:
Let the speed of Sameer in still water be x km/h
Sameer's speed downstream = (x + 12) km/h
Sameer's speed upstream = (x - 12) km/h
According to the question, 24(x + 12) = 36(x - 12)
? 2x + 24 = 3x - 36
? x = 36 + 24 = 60 km/h
Correct Answer: 1 km/h
Explanation:
Let speed of the flow of water be x km/h and rate of sailing of sailor be y km/h.
Downstream speed (x + y) = 48/8
? x + y = 6 ....(i)
and upstream speed x - y = 4 ...(ii)
On solving Eqs. (i) and (ii), we get
y = 1 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: 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: 8 km/h
Explanation:
Speed 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
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
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