3. Find the largest possible volume of the tetrahedron PQRS, where P(1,0,0), Q(0,2,0), R(0,0,3) and S lies on the unit sphere centered at the origin.

1. There was a class of 41 people divided into three groups A, B, and C, and the average score of subject natural’s test was 89.7 points; the average score of group A was 89.8 points; the average score of A, B combination was 88.5 points; the average score of A and C combination was 91 points, and how many people were in each of groups A, B and C?