Problema Solution
Sandy paddled a canoe 20 miles upstream then paddled back. If the rate of the current was 3mph and the total trip took 7 hours, what was her rate?
Answer provided by our tutors
Let x = rate
Let y = time she spent on first leg
(x-3)*y = 20
(x+3) * (7-y) = 20
y = 20/(x-3)
(x+3)*(7-20/(x-3)) = 20
(x-7)(7x+9)/ (x-3) = 0
x = 7
x = -9/7 (reject)
So the rate is 7 mph
She went 7 mph - 3 mph current = 4 net mph for 5 hours on the first leg
She went 7 mph + 3 mph current = 10 mph for 2 hours on the second leg, for 7 hours total.