Answer
This is a sphere of radius 2.5 cm.
Work Step by Step
This problem is fairly difficult to draw but not too hard to describe. Recall, a locus is equidistant from the original sphere at all points. In addition, the book wants the midpoint of the radius, so it follows that the new points are half of the radius away from the center of the sphere, and they are the same distance away from the edge of the sphere. This is a sphere of radius 2.5 cm.