SOLUTION: A boat traveled 210 miles downstream and back ( 210 miles each way ). The trip downstream took 10 hours. The trip back took 70 hours. What is the speed of the boat in still wate

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: A boat traveled 210 miles downstream and back ( 210 miles each way ). The trip downstream took 10 hours. The trip back took 70 hours. What is the speed of the boat in still wate      Log On


   

Question 110023: A boat traveled 210 miles downstream and back ( 210 miles each way ). The trip downstream took 10 hours. The trip back took 70 hours. What is the speed of the boat in still water? What is the speed of the current?
For the current speed I came up with the answer of 8.3 mph. But I could not figure out the speed of the boat in still water.
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
let b=boat, c=current ... b+c=210/10 ... b+c=21 ... b-c=210/70 ... b-c=3

(b+c)+(b-c)=21+3 ... 2b=24 ... b=12

12+c=21 ... c=9