0.125乘以0.25乘以0.5乘以64用简便计算怎么做?399.6乘以9—1998乘以0.求求你们了

0.125乘以0.25乘以0.5乘以64
＝0.125x8x0.25x4x0.5x2
=1x1x1
=1
399.6乘以9—1998乘以0.8
=1998x0.2x9-1998x0.8
=1998x1.8-1998x0.8
=1998x(1.8-0.8)
=1998