Answer:
13 mph
Step-by-step explanation:
You want the speed of a boat that travels 17 miles downstream with a 4 mph current in the same time it travels 9 miles upstream against that current.
Time, Speed, Distance
The relation between time, speed, and distance is ...
[tex]t=\dfrac{d}{s}[/tex]
For the time to be the same for both trips, we must have ...
[tex]\dfrac{17}{b+4}=\dfrac{9}{b-4}\\\\17(b-4)=9(b+4)\\\\8b=(17+9)(4)=104\\\\b=104/8=13[/tex]
The speed of the boat is 13 miles per hour in still water.
