SOLUTION: A river has a current speed of 5 miles per hour. A boat travels down river for 20 miles. It then makes the return trip up the river. If the return trip took 8 hours and 20 minutes

Question 1159172: A river has a current speed of 5 miles per hour. A boat travels down river for 20 miles. It then makes the return trip up the river. If the return trip took 8 hours and 20 minutes longer than the trip down river, what is the speed of the boat in still water?
Found 4 solutions by josgarithmetic, MathTherapy, greenestamps, ikleyn:
Answer by josgarithmetic(39616)   (Show Source): You can put this solution on YOUR website!
r, speed of boat in still water

--------solve for r.

Divide both sides by 5, multiply both sides by 3,

.
.

-

....
AMP Parsing Error of [highlight(r=)]: Invalid expression ')': syntax error at /home/ichudov/project_locations/algebra.com/templates/Algebra/Expression.pm line 203. .

Answer by MathTherapy(10551)   (Show Source): You can put this solution on YOUR website!

A river has a current speed of 5 miles per hour. A boat travels down river for 20 miles. It then makes the return trip up the river. If the return trip took 8 hours and 20 minutes longer than the trip down river, what is the speed of the boat in still water?

Correct answer: Speed of boat in still water:
Answer by greenestamps(13198)   (Show Source): You can put this solution on YOUR website!

If r is the speed in mph of the boat in still water, then its upstream speed is r-5 and its downstream speed is r+5.

upstream time: 20/(r-5)
downstream time: 20/(r+5)

The upstream time is 8 1/3 hours (25/3 hours) greater than the downstream time:

Multiply everything by the least common denominator, 3(r-5)(r+5):

(clearly the r = -7 solution makes no sense...)

ANSWER: The speed of the boat in still water is 7mph

CHECK:
upstream speed: 20/(7-5) = 20/2 = 10
downstream speed: 20/(7+5) = 20/12 = 5/3 = 1 2/3
10 - 1 2/3 = 8 1/3

Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!

RELATED QUESTIONS
A speedboat travels 26 miles up a river (against the current), then makes the return trip (answered by stanbon)
A boat travels 24 miles up the river in same amount of time it takes to travel 32 miles... (answered by josgarithmetic)
A boat travels 12 miles up the Mississippi River and 12 miles back down river in a total... (answered by mananth,josmiceli)
A BOAT TRAVELS 52 MILES UP THE RIVER IN THE SAME AOUNT OF TIME IT TAKES TO TRAVEL 92... (answered by solver91311)
a boat trip trip 10 miles down a river takes you 1 hour and 15 minutes but it takes 4... (answered by solver91311)
a boat can travel 18 miles up a river in the same amount of time it takes to travel 42... (answered by ankor@dixie-net.com)
A boat takes 1 hour to travel 12 miles down river (with the current). Against the same... (answered by ikleyn)
A motorboat heads upstream on a river that has a current of 3 miles per hour.The trip... (answered by josgarithmetic)
How in the world do you set this guy up? A boat travels 25 miles per hour in still... (answered by TimothyLamb)