Question

用简便方法计算下面各题．2.3×2.5×0.40.29×1021.2×2

用简便方法计算下面各题．2.3×2.5×0.40.29×1021.2×2.5+0.8×2.51.25×0.4×8×2.50.125×720.25×39+0.25．

Answer 1

（1）2.3×2.5×0.4
=2.3×（2.5×0.4）
=2.3×1
=2.3；

（2）0.29×102
=0.29×（100+2）
=0.29×100+0.29×2
=29+0.58
=29.58；

（3）1.2×2.5+0.8×2.5
=（1.2+0.8）×2.5
=2×2.5
=5；

（4）1.25×0.4×8×2.5
=（1.25×8）×（0.4×2.5）
=10×1
=10；

（5）0.125×72
=0.125×（8×9）
=0.125×8×9
=1×9
=9；

（6）0.25×39+0.25
=0.25×39+0.25×1
=0.25×（39+1）
=0.25×40
=10．