Question
A motorboat whose speed is 15 km/hr on still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is :
Answer: Option B
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Let he speed of the stream be `x` m/hr, Then
Speed downstream = `(15 + x)` km/hr,
Speed upstream = `(15 - x)` m/hr
`:.` `30/(15 + x) + 30/(15 - x) = 4 1/2`
`hArr (900)/(225 - x^2) = 9/2`
`hArr 9 x^2 = 225 `
`hArr x^2 = 25 hArr x` = 5 km/hr
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