math algebra
posted by alms on .
Paul Websters motorboat can travel 15 mph in still water. Traveling with the current of a river, the boat can travel 20 miles in the same time it takes to go 10 miles againt the current. Find the speed of the current.

(15+Vc)t = 20
Eq1: 15t + Vc*t = 20
(15Vc)t = 10
Eq2: 15t  Vct = 10
Add Eq1 and Eq2:
15t + Vct = 20
15t _ Vct = 10
30t = 30
t = 1 h.
15*1 + Vc*1 = 20
Vc = 2015 = 5 mi/h. = Velocity of current.