How far is the center of mass of the earth-moon system from thecenter of the earth? (appendix c gives the masses of the earth andthe moon and the distance between the two.)

from the center of the earth.

Explanation:

We have a system of Earth & Moon:

Now we assume the origin of the system to be at the center of the earth.

Now for the center of mass of this system:

here:

are the distance of the centers (center of masses) of the Earth and the Moon from the origin of the system.

∵ since we have taken the point as the origin of the system.

now putting the values in the above equation:

from the center of the earth.