<PRE><B>Question 968623</B>
Julie and Eric row their boat( at a constant speed) 63 miles downstream for 7 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current.
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let x=rowboat speed in still water(current=0)
let c=speed of current
x+c=rowboat speed with current
x-c=rowboat speed against current
travel time*speed =distance
..
7(x+c)=63
9(x-c)=63
..
7x+7c=63
9x-9c=63
..
63x+63c=567 (mult. eq by 9)
63x-63c=441 (mult. eq by 7)
subtract:
126c=126
c=1
rate of the current=1 mph</PRE>