<PRE><B>Question 1167838</B>
speed downstream is s+c and (s+c)*t=11
speed upstream is s-c and (s-c)*t=7; so in 4 hours (s-c)*4+5=(s+c)*3
we know that t=11/(s+c) and t=7(s-c)
so that 11s-11c=7s+7c
so that 4s=18c
or 2s=9c
or s=4.5c

Therefore, s-c=3.5 c
and 14c+5=16.5c
and 2.5c=5 and c=2 mph

s then is 9 mph, so that 3 hours downstream is 33 miles and 4 miles upstream is 28 miles. That checks.

11 miles downstream takes 1 hour, and that is the same time it takes him to row 7 miles upstream

The answer is 2 mph.
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