Question 169828
BELIEVE YOU LEFT OUT THE HOUR FIGURE????
The speed of the current in a river is 2mph.  Jay travels 20 miles upstream and then 20 miles downstream in a total time of 5 1/3 hours.  Find the speed of the boat. Let s be the speed of the boat.
D=ST
T=D/S
5.33=20/(S-2)+20/(S+2)
5.33=(20[S+2]+20[S-2])/(S+2)(S-2)
5.33=(20S+40+20S-40)/(S^2-4)
5.33=40S/(S^2-4)
5.33S^2-21.333=40S
5.33S^2-40S-21.333=0
uSING THE QUADRATIC EQUATION{{{S=(-b+-sqrt(b^2-4*a*c))/(2*a)}}}WE GET:
S=(40+-SQRT[-40^2-4*5.33*-21.333])/2*5.333
S=(40+-SQRT[1,600+455])/10.6667
S=(40+-SQRT2,055)/10.6667
S=(40+-SQRT45.333)/10.667
S=(40+45.333)/10.667
S=85.333/10.667
S=8 MPH. ANS FOR THE SPEED OF THE BOAT IN CALM WATERS.