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