SOLUTION: in the rafting situation, a boat goes 30 kilometer downstream in 75 minutes and the same distance up stream in 90 minutes, calculate the speed of the stream in kilometer per hour.

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Question 328732: in the rafting situation, a boat goes 30 kilometer downstream in 75 minutes and the same distance up stream in 90 minutes, calculate the speed of the stream in kilometer per hour.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Rate*Time=Distance
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Let V be the speed of the raft in still water and S be the speed of the stream.
1.%28V%2BS%2975=30<--- with the stream
2.%28V-S%2990=30<--- against the stream
From eq.1,
V%2BS=30%2F75=2%2F5
From eq. 2,
V-S=1%2F3
Subtract the second from the first to eliminate V.
V%2BS-V%2BS=2%2F5-1%2F3
2S=6%2F15-5%2F15
S=2%2F15 km/min
Since there are 60 minutes in 1 hr.
S=%282%2F15%29%2860%29
highlight%28S=8%29kph