SOLUTION: A sailboat travels 20 miles downstream in three hours. It returns in four hours. Find the speed of the sailboat in still water AND the rate of the current.

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This is a speed and distance problem. The assumption here is the speed of the sailboat is the same in both direction. The current however will help travel downstream and low travel upstream. The distance travelled in each direction will be the same.
where s=speed of sailboat and c=speed of current
downstream would be

coming back upstream

If we solve the second equation for s we get

Divide both sides by 4

Simplify

Using substitution, replace s with 5+c in first equation

Distribute to remove parenthesis

Move constants to one side and combined like variables


divide both sides by 6

mph
Put this value for c back into s=5+c
mph