Question
Download Solution PDFThe speed of a boat in still water is 15 km/hr. If it can travel 42 km downstream and 28 km upstream in the same time, then what is the speed of the stream ?
Answer (Detailed Solution Below)
Detailed Solution
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42 / (15 + x) = 28 / (15 - x)
⇒ 3(15 - x) = 2(15 + x)
⇒ x = 3 km/h
Therefore, the speed of the stream is 3 km/hr.
Alternate Method
Formula used:
Time = Distance / Speed
Calculation:
Let's assume the speed of the stream is 'x' km/hr.
When the boat travels downstream. So
Relative Speed = (15 + x) km/hr
When the boat travels upstream. So
Relative speed = (15 - x) km/hr
We know that
Time = Distance / Speed
⇒ 42 /(15 + x) = 28 /(15 - x)
⇒ 42(15 - x) = 28(15 + x)
⇒ 630 - 42x = 420 + 28x
⇒ 70x = 630 - 420
⇒ x = 3
Therefore, the speed of the stream is 3 km/hr.
Last updated on Jun 26, 2025
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