coordinate geometry problem

In coordinate geometry:
Given the midpoints of the sides of a triangle: P(2,5), Q(4,2) and R(1,1)
Find the coordinates of the vertices.

And tell me how you solved it.

Midpoint between 2 points (X1,Y1) and (X2,Y2) is ((X1+X2)/2,(Y1+Y2)/2).
I'd make 3 points (X1,Y1),(X2,Y2),(X3,Y3) and then you can create a system of equations that you can easily solve.