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.