Question 154657
DISTANCE=RATE*TIME OR DISTANCE/TIME=RATE
20/3=6.666 WITH THE CURRENT.
20/4=5 AGAINST THE CURRENT.
(6.666-5)/2=1.666/2=.833MPH IS THE SPEED OF THE CURRENT.
PROOF:
6.666-.833=5.833 SPEED OF THE SAIL BOAT.
5+.833=5.833 DITTO.