解题思路:(1)运用加法交换律简算;
(2)运用乘法分配律简算;
(3)根据减法的性质简算;
(4)运用加法的交换律;
(5)先根据乘法的意义得出25×(98+98+98+98)=25×(98×4),然后乘法的结合律简算;
(6)先算小括号里面的加法,再算小括号外面的减法;
(1)50.34+11.645-42.34,
=50.34-42.34+11.645,
=8+11.645,
=19.645;
(2)99+99×99,
=99×(1+99),
=99×100,
=9900;
(3)8.64-(2.75+3.64)
=8.64-2.75-3.64
=8.64-3.64-2.75
=5-2.75
=2.25
(4)15.07-7.34+20.93
=15.07+20.93-7.34
=36-7.34
=28.66;
(5)25×(98+98+98+98)
=25×(98×4)
=25×4×98
=100×98
=9800;
(6)108.12-(39.5+46.24)
=108.12-85.74
=22.38
点评:
本题考点: 小数四则混合运算;整数四则混合运算;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.