Boats and Streams problems
- 1. A swimmer's speed downstream is 11 km/h and speed of the stream is 1.5 km/h. Find the upstream speed of swimmer.?
Options- A. 8 km/h
- B. 9.5 km/h
- C. 9 km/h
- D. 6. 25 km/h Discuss
Correct Answer: 8 km/h
Explanation:
Rate of stream = ( Speed downstream - Speed upstream )/2
? 1.5 = (11 - Speed upstream)/2
? 11 - Speed upstream = 3
? Speed upstream = 11 - 3 = 8 km/h
- 2. A boat goes 48 km downstream in 20 h. It takes 4 h more to cover the same distance against the stream. What is the speed of the boat in still water?
Options- A. 2.2 km/h
- B. 2 km/h
- C. 4 km/h
- D. 4.2 km/h Discuss
Correct Answer: 2.2 km/h
Explanation:
Speed downstream = 48/20 = 2.4 km/h
Speed upstream = 48/24 = 2 km/h
? Speed of boat in still water = (Speed downstream + Speed upstream)/2
= (2.4 + 2)/2 = 4.4/2 = 2.2 km/h
- 3. Keshav can row 60 km downstream and 36 km upstream, taking 10 h each time. What is the velocity of the current?
Options- A. 3 km/h
- B. 2. 2 km/h
- C. 4 km/h
- D. 1.2 km/h Discuss
Correct Answer: 1.2 km/h
Explanation:
Speed upstream = Distance/Time = 60/10 = 6 km/h
Speed upstream = Distance/Time = 36/10 = 3.6 km/h
? Velocity of the current = (speed downstream - Speed upstream)/2
= (6 - 3.2)/2 = 1.2 km/h
- 4. What time will be taken by a boat to cover a distance of 128 km along the stream, if speed of a boat in still water is 24 km/h and speed of stream is 8 km/h?
Options- A. 8 km/h
- B. 4 km/h
- C. 7 km/h
- D. 6 km/h Discuss
Correct Answer: 8 km/h
Explanation:
Downstream speed of boat = Speed of boat in still water + Speed of stream
= 24 + 8 = 32 km/h
? Required time = Distance/Speed downstream
= 128/32 = 4 km/h
- 5. 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?
Options- A. 13 km/hr
- B. 2.25 km/hr
- C. 17 km/hr
- D. 15 km/hr Discuss
Correct Answer: 17 km/hr
Explanation:
? (12 x 60)/48 = (L - 2)
? L = 15 + 2 = 17 km/hr
- 6. The current of a stream runs at the rate of 4 km/hr. A boat goes 6 km and back to the starting point in 2 hours. The speed of the boat in still water is?
Options- A. 6 km/hr
- B. 7.5 km/hr
- C. 8 km/hr
- D. 6.8 km/hr Discuss
Correct Answer: 8 km/hr
Explanation:
Let the speed in still water be x km/hr
Then, 6/x + 4 + 6/x - 4 = 2
? 6[ x - 4 + x + 4] = 2(x2 - 16)
? x2 - 6x - 16 = 0
? (x - 8) (x + 2) = 0
? x = 8 km/hr
- 7. A boat moves upstream at the rate of 1 km in 10 minutes and downstream at the rate of 1 km in 6 minutes. The speed of the current is?
Options- A. 1 km/hr
- B. 1.5 km/hr
- C. 2 km/hr
- D. 2.5 km/hr Discuss
Correct Answer: 2 km/hr
Explanation:
Speed upstream = 6 km/hr
Speed downstream = 10 km/hr
? Speed of the current = (10 - 6)/2 km/hr = 2 km/hr
- 8. A man rows upstream 16 km and downstream 28 km talking 5 hours each time. The velocity of the current is?
Options- A. 2.4 km/hr
- B. 1.2 km/hr
- C. 3.6 km/hr
- D. 1.8 km/hr Discuss
Correct Answer: 1.2 km/hr
Explanation:
Speed downstream = (28/5) km/hr = 5.6 km/hr
Speed upstream = (16/5) km/hr = 3.2 km/hr
Velocity of current = (5.6 - 3.2)/2 km/hr = 1.2 km/hr
- 9. A man can row at 5 km/hr in still water and the velocity of current is 1 km/hr. It takes him 1 hour to row to a place and back. How far is the place?
Options- A. 2.5 km
- B. 2.4 km
- C. 3 km
- D. 3.6 km Discuss
Correct Answer: 2.4 km
Explanation:
Speed downstream = (5 + 1) km/hr = 6 km/hr
Speed upstream = (5 - 1) km/hr = 4 km/hr
Let the required distance be d km
Then, d/6 + d/4 = 1
? 2d + 3d = 12
? d = 2.4 km
- 10. A man can row 44 km downstream in 4 hours. If the man's rowing rate in still water is 8 km/hr, then find in what time will he cover 25 km upstream?
Options- A. 5 hours
- B. 6 hours
- C. 4.5 hours
- D. 4 hours Discuss
Correct Answer: 5 hours
Explanation:
? Man's rate in still water = (man's rate with current + his rate against current)/2
? 8 = 1/2 [ 44/4 + 25/T ]
? 16 = 11 + 25/T
? T = 5 hours
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