Solution to Exercise 3

1 & 2. Using the generalized form of Kepler's 3rd law,

(m1 + m2) P2 = (a1 + a2) 3
or
P2 = (a1 + a2) 3 / (m1 + m2)
it is clear that the period must become shorter if one of the masses is increased.

The ratio of the distances from the center of mass is the same ratio as that of the masses, with the larger mass star being closer to the cm and having the smaller orbit and the smaller mass star having the larger orbit because of its greater distance from the cm.