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March 1, 2015

March 1, 2015

Posted by **Sandra** on Friday, July 17, 2009 at 1:40am.

Upstream, downstream. Junior’s boat will go 15 miles per

hour in still water. If he can go 12 miles downstream in the

same amount of time as it takes to go 9 miles upstream,

then what is the speed of the current?

- algebra -
**Reiny**, Friday, July 17, 2009 at 7:43amlet the speed of the current be x mph

so the time taken to go 9 miles upstream (against the current) = 9/(15-x)

and the time taken to go 12 miles downstream (with the current) = 12/(15+x)

but we are told the times are the same, so

12/(15+x) = 9/(15-x)

cross-multiply

solve for x to get the speed (I got around 2.14)

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