Problema Solution
Abby rows 10 km upstream and 10km back in a total of 3hrs. The speed of the river is 5 km/h. Find Abby's speed in still water.
Answer provided by our tutors
10km / (x+5)km/hr + 10km / (x-5)km/hr = 3hr
10/(x+5) + 10/(x-5) =3
multiply both sides by (x+5) and (x-5)
10x+50 + 10x-50 = 3(x+5)(x-5)
20x = 3x^2 +15x - 15x -75
3x^2 -20x - 75 = 0
use the quadratic formula to finish
x = 9.3426 or -2.6759 and since speed can't be negative it has to be the 9.3426 answer