SOLUTION: Julie and Eric row their boat (at constant speed ) 40 miles downstream for 4 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 10 hours

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Julie and Eric row their boat (at constant speed ) 40 miles downstream for 4 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 10 hours      Log On


   

Question 1017321: Julie and Eric row their boat (at constant speed ) 40 miles downstream for 4 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 10 hours. Find the rate of the current.
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39625) About Me  (Show Source):
You can put this solution on YOUR website!
RT=D travel rates rule 

                   rate       time        distance
Down               40+c        4           d
Up                 40-c        10          d


RT=D
R=D/T
system%2840%2Bc=d%2F4%2C40-c=d%2F10%29

OR much simpler, %2840%2Bc%29%2A4=%2840-c%29%2A10.
Solve this for c.

Answer by MathTherapy(10555) About Me  (Show Source):
You can put this solution on YOUR website!

Julie and Eric row their boat (at constant speed ) 40 miles downstream for 4 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 10 hours. Find the rate of the current.
Let speed in still water be S, and speed of current, C

Then, downstream speed equation is: S+%2B+C+=+40%2F4______S + C = 10______S = 10 - C ------- eq (i)

Also, upstream speed equation is: S+-+C+=+40%2F10______S - C = 4 ------- eq (ii)

10 - C - C = 4 ------- Substituting 10 - C for S in eq (ii)

      - 2C = 4 - 10

      - 2C = - 6

C or speed of current = %28-+6%29%2F%28-+2%29, or highlight_green%28matrix%281%2C2%2C3%2Cmph%29%29