<PRE><B>Question 1078008</B>
 the boat can travel 35 miles upstream in 7 hours.
 If boat can go 63 miles downstream in the same a time, how fast is the river current?
:
let s = boat speed in still water
let c = the rate of the current
from the information given, we can find the effective speed each way
 35/7 = 5 mph upstream
and
 63/7 = 9 mph down stream
two equations, we can use elimination to find c
s + c = 9 
s - c = 5
-------------Subtraction eliminates s
0 + 2c = 4
c = 2 mph is speed of the river
:
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