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A boat goes downstream and covers the distance between two ports in 4 hours, while it covers the same distance upstream in 5 hours. If the speed of the stream is 2km/hour. what is the speed of boat in still water ?
  • a)
    18 km/hour
  • b)
    16 km/hour
  • c)
    20 km/hour
  • d)
     15 km/hour 
Correct answer is option 'A'. Can you explain this answer?
Verified Answer
A boat goes downstream and covers the distance between two ports in 4 ...
Let the speed of boat in still water be x km/hour. 
∴ (x + 2) 4 = (x – 2) 5
⇒  4x + 8 = 5x - 10
⇒ x = 18 km/hr
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Most Upvoted Answer
A boat goes downstream and covers the distance between two ports in 4 ...
To solve this problem, we need to understand the concept of relative speed. The speed of the boat in still water can be determined by considering the speed of the boat relative to the stream.

Let's assume the speed of the boat in still water is 'x' km/hour and the speed of the stream is 2 km/hour.

1. Speed downstream:
When the boat is moving downstream, the speed of the stream adds to the speed of the boat, so the effective speed is (x + 2) km/hour.
Given that the boat covers the distance between two ports in 4 hours, we can write the equation:
Distance = Speed × Time
Distance downstream = (x + 2) × 4

2. Speed upstream:
When the boat is moving upstream, the speed of the stream subtracts from the speed of the boat, so the effective speed is (x - 2) km/hour.
Given that the boat covers the same distance between the two ports in 5 hours, we can write the equation:
Distance = Speed × Time
Distance upstream = (x - 2) × 5

Since the distance covered is the same in both cases, we can equate the two equations:
(x + 2) × 4 = (x - 2) × 5

Simplifying this equation, we get:
4x + 8 = 5x - 10
8 + 10 = 5x - 4x
18 = x

Hence, the speed of the boat in still water is 18 km/hour. Therefore, the correct answer is option A.
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A boat goes downstream and covers the distance between two ports in 4 hours, while it covers the same distance upstream in 5 hours. If the speed of the stream is 2km/hour. what is the speed of boat in still water ?a)18 km/hourb)16 km/hourc)20 km/hourd)15 km/hourCorrect answer is option 'A'. Can you explain this answer?
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