递等式计算(能简便的用简便方法).

1个回答

  • 解题思路:(1)去括号,利用乘法交换律和结合律进行简算;

    (2)按运算顺序进行计算,不要先算成70.8-0.8;

    (3)不能简算,按运算顺序进行计算;

    (4)去括号后,把40拆成8×5,与12.5进行简算;

    (5)利用减法的性质,把原式变为4.12-(1.78+1.22);

    (6)利用除法的性质简算.

    (1)12.5×(0.7×0.8),

    =12.5×0.8×0.7,

    =10×0.7,

    =7;

    (2)70.8-0.8×0.5,

    =70.8-0.4,

    =70.4;

    (3)13-3.79+6.21,

    =9.21+6.21,

    =15.42;

    (4)12.5×(40+0.7),

    =12.5×8×5+12.5×0.7,

    =500+8.75,

    =508.75;

    (5)4.12-1.78-1.22,

    =4.12-(1.78+1.22),

    =4.12-3,

    =1.12;

    (6)4.2÷0.7÷6,

    =4.2÷(0.7×6),

    =4.2÷4.2,

    =1.

    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: 此题主要考查对四则运算的灵活性,要做到计算灵活就要熟练地掌握四则运算的法则、定律以及运算性质.