The median is the line joining a vertex of the triangle to the side opposite it. The point where the 3 medians meet is the centroid. The centroid divides the median in the ratio of 2/3
This means that
OB = 2/3BF
From the information given,
OB = 10
Thus,
10 = 2BF/3
By crossmultiplying,
2BF = 3 x 10 = 30
BF = 30/2 = 15
OF + OB = BF
OF + 10 = 15
OF = 15 - 10
OF = 5
