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

1个回答

  • 解题思路:(1)运用乘法交换律简算;

    (2)先把102分解成100+2,再运用乘法分配律简算;

    (3)运用乘法分配律简算;

    (4)运用乘法交换律和乘法结合律简算;

    (5)先把72分解成8×9,再运用乘法结合律简算;

    (6)先把后一个0.25分解成0.25×1,再运用乘法分配律简算.

    (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.

    点评:

    本题考点: 小数四则混合运算;运算定律与简便运算.

    考点点评: 此题是考查四则混合运算,要仔细观察算式的特点,灵活运用一些定律进行简便计算.