99.9×7.8+33.3×6.61
＝33.3×3×7.8+33.3×6.61
＝33.3×23.4+33.3×6.61
＝33.3×（23.4+6.61）
＝33.3×30.01
＝33.3×30+33.3×0.1
＝999+0.333
＝999.333
99.9×7.8+33.3×6.61
＝33.3×3×7.8+33.3×6.61
＝33.3×23.4+33.3×6.61
＝33.3×（23.4+6.61）
＝33.3×30.01
＝33.3×30+33.3×0.1
＝999+0.333
＝999.333