Question 209211
Julie and Eric row their boat (at a constant speed) 45 miles downstream for 5 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.


The speed that they travelled at, downstream, with the current = 9 mph (45/5) 


The speed that they travelled at, upstream, against the current = 5 mph (45/9) 


Let the rate of the current be C


Then we'll have: Downstream speed - current = Upstream speed + current, or,


9 - C = 5 + C


- 2C  =  - 4

{{{C = (-4)/-2 = 2}}}

Therefore, the speed of the current is: {{{highlight_green(2)}}} mph.