考点:整数、分数、小数、百分数四则混合运算,运算定律与简便运算
专题:运算顺序及法则,运算定律及简算
分析:(1)先算括号内的,再算括号外的除法,最后算加法.
(2)运用乘法分配律简算前一项,最后算加法.
(3)先算小括号内的,再算中括号内的,最后算括号外的.
(4)把除法变为乘法,运用乘法分配律简算.
(5)运用除法的性质简算.
(6)(7)(8)运用乘法分配律简算.
(9)把每个分数拆成两个分数相减的形式,然后通过加减相互抵消,求得结果.
(10)先计算括号内的,然后通过约分计算即可.
解答:
解:(1)12+1÷(1-
)
=12+1÷
=12+4
=16
(2)(
-
)×21+
=
×21-
×21+
=14-12+
=2+
=2
(3)
÷[(
+
)×4]
=
÷[
×4]
=
÷
=
×
=
(4)
×15+1÷
=
×15+
=
×(15+1)
=
×16
=6
(5)
÷
+
÷
=(
+
)÷
=1÷
=
(6)24-24×
=24×(1-
)
=24×
=
(7)(
-
)×21
=
×21-
×21
=35-6
=29
(8)17×21×(
-
)
=17×21×
-17×21×
=210-68
=142
(9)1-
-
-
-
-
-
=1-
-(
-
)-(
-
)-(
-
)-(
-
)-(
-
)
=1-
-
+
=
(10)1980÷(1980+
)
=1980÷(
)
=1980×
=
点评:此题考查了分数的四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律或运算技巧简便计算.