SOLUTION: assen can travel miles downstream in his motorboat in the same time he travels 3 miles upstream. if the current of the river is 3 mph, what is the boats rate in still water? write

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: assen can travel miles downstream in his motorboat in the same time he travels 3 miles upstream. if the current of the river is 3 mph, what is the boats rate in still water? write      Log On


   

Question 971783: assen can travel miles downstream in his motorboat in the same time he travels 3 miles upstream. if the current of the river is 3 mph, what is the boats rate in still water? write an equation that could be used to model this problem. let r represent the boats rate (in mph) in still water?
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
You missed a datum in the description. Not too bad an omission; I will generalize.

r, speed of boat for still water, UNKNOWN
c, speed of river current
d, distance going downstream
u, distance going upstream
t, time to travel either direction, UNKNOWN


___________________rate___________time__________distance
UPSTRM_____________r-c____________t_____________u
DOWNSTR____________r+c____________t_____________d

system%28%28r-c%29t=u%2C%28r%2Bc%29t=d%29

system%28t=u%2F%28r-c%29%2Ct=d%2F%28r%2Bc%29%29

u%2F%28r-c%29=d%2F%28r%2Bc%29

u%28r%2Bc%29=d%28r-c%29

ur%2Buc=dr-dc

ur-dr=-dc-uc

dr-ur=dc%2Buc, which makes sense for the signs

r%28d-u%29=dc%2Buc

highlight%28r=%28dc%2Buc%29%2F%28d-u%29%29