Question

Don Williams uses his small motorboat to go 5 miles upstream to his favorite fishing spot. Against the current, the trip takes 1/3 hour. With the current the trip takes 1/5 hour. How fast can the boat travel in still water?

Answer 1

12 MPH GOING UP STREAM.

Answer 2

Suppose x is the rate at which the boat travels at still water.
let y be rate in moving water
up stream is x-y 
down stream is x+y
the 1/3(x-y)=5
1/5(x+y)=5
solve the system
x-y=15
x+y=25
add the equation to cancel y
we get 2x=40
x=20 
therefore the boat is moving at rate of 20 miles for hour in still water