Exercise 2: Star Masses

If we determine for a binary system that the period is 40 years and the average separation is 25 AU, what is the total mass of the binary system? You may find it useful to use the Kepler's Law Calculator in doing this problem.
Why do we need to know the true distance to a visual binary in order to compute the masses of the stars?
How could an astrometric binary become a visual binary?

The Solutions