Take BC as the X axis, point A as any point not on the X axis, and connect A, B and C to form a triangle. The area of the triangle = 1/2, and the base x is high. When the area of △PBC is exactly equal to S/4, the Y-axis coordinate of point P only needs to be a quarter of the Y-axis coordinate of point A. We assume that the coordinate of point A is (m, n), then the area of point G and the part below the line fg is the area of point P that satisfies the meaning of the question. Let it be k, and according to the geometric probability, the probability that the area of △Pbc is less than S/4 is the area of k divided by s, and the area of k can be obtained by similar triangles's theorem. If point A is the high intersection of bc, y=n/4 is at point D, and BC is at point E, then AD/AE = 3/4, S △ AFG/.