4/9x1/2 5/12x8/9 1/2x2/3 7/15x5/7
4/9×1/2 = 4/18 = 2/9 5/12×8/9 = 5/3×2/9 = 10/27 1/2×2/3 = 1/3 7/15×5/7 = 1/3 ×1/1 = 1/3