A river flows at the rate of 2 mph. If a motorboat can travel 12 miles upstream and return in a total of 2.5 hours, what is the speed of the motorboat in still water?

Answer 1

d / r = t

[12 / (m - 2)] + [12 / (m + 2)] = 2.5

12(m + 2) + 12(m - 2) = 2.5(m^2 - 4)

0 = 2.5 m^2 - 24 m - 10

use quadratic formula to find m