SOLUTION: Julie's whaler cruised 45 miles upstream and 45 miles back in a total of 8 hr. the speed of the river is 3mph. Find the speed of the boat in still water. having problems settin

Question 43354: Julie's whaler cruised 45 miles upstream and 45 miles back in a total of 8 hr. the speed of the river is 3mph. Find the speed of the boat in still water.
having problems setting this up
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Julie's whaler cruised 45 miles upstream and 45 miles back in a total of 8 hr. the speed of the river is 3mph. Find the speed of the boat in still water.
Let the speed of the boat in still water be "b"
Upstream DATA:
distance= 45; rate=b-3;time=d/r=45/(b-3)
Downstream DATA:
distance= 45; rate=b+3; time=d/r=45/(b+3)
EQUATION:
Time Up + Time Down = 8 hrs.
45/(b-3) + 45(b+3)= 8
45(b+3) + 45(b-3)=8(b^2-9)
90b=8b^2-72
8b^2-90b-72=0
4b^2-45b-36=0
b=[45-sqrt(45^2-4(4)(-36)]/8=[45-38.0657]/8=0.86678... mph
OR
b=[45+sqrt(45^2-4(4)(-36)]/8=[45+38.0657]/8=10.3832... mph
Cheers,
stan H.
RELATED QUESTIONS
Julia's Boston Whaler cruised 45 miles upstream and 45 miles back in a total of 8 hours.... (answered by ikleyn)

Jens boat cruised 45 miles upstream and 45 miles back in a total of 8 hr. The speed of... (answered by ankor@dixie-net.com)

Jen�s boat cruised 45 miles upstream and 45 miles back in a total of 8 hr. The speed of (answered by nerdybill,stanbon,richwmiller)

Jen's boat cruised 45 miles upstream and 45 miles back in a total of 6 hrs. The speed of (answered by scott8148)

The question is: A river has a current of 3mph. A boat goes 35 miles upstream in the same (answered by stanbon,oberobic)

The current in a stream moves at a speed of 3mph. A boat travels 45 miles upstream and... (answered by stanbon)

sammy owns a motor boat that travels 4 miles/hour in still water. It goes 12 miles... (answered by mananth)

The current in a stream moves at a speed of 3mph. A boat travels 45mi upstream and 45 mi... (answered by checkley77,dabanfield)

Sara decides to canoe 3 miles upstream on a river to a waterfall and then come back.... (answered by stanbon)