<PRE><B>Question 880553</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 current
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let x=constant speed of boat
let c=speed of current
x+c=speed of boat traveling with the current
x-c=speed of boat traveling against the current
travel time=distance/speed
..
{{{63/(x+c)=7}}}
{{{63/(x-c)=9}}}
..
7x+7c=63
9x-9c=63
..
63x+63c=567 (mult. by 9)
63x-63c=441 (mult. by 7)
subtract:
126c=126
c=1
rate of current=1 mph</PRE>