Arowing team rowed 90 miles while going with the current in the same amount of time as it took to row 10 miles going against the current. the rate of the current was 4 miles per hour. find the rate of the rowing team in still water.

   
 let x=rate of the rowing team in still water 
 x+4=rate of the rowing team with current 
 x-4=rate of the rowing team against current   
 travel time=distance/rate 
 .. 
 90%2F%28x%2B4%29=10%2F%28x-4%29 
 90x-360=10x+40 
 80x=400 
 x=5  rate of the rowing team in still water=5 mph

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