B2. Given 19 points in the plane with integer coordinates, no three collinear, show that we can always find three points whose centroid has integer coordinates.
B3. ABC is a triangle with ∠C = 90o. E is a point on AC, and F is the midpoint of EC. CH is an altitude. I is the circumcenter of AHE, and G is the midpoint of BC. Show that ABC and IGF are similar.
To avoid possible copyright problems, I have changed the wording, but not the substance, of the problems.