9.9*15=(10-0.1)*15=10*15-0.1*15=150-1.5=148.5
9.9×1.5 =(10-0.1)×1.5 =10× 1.5-1.5× 1=15-1.5=13.5
9.9*15=(10-0.1)*15=150-1.5=148.5
9.9X15=10X15-0.1X15