考点:小数四则混合运算,分数的四则混合运算,方程的解和解方程,解比例
专题:运算顺序及法则,运算定律及简算
分析:(1)先算乘除法,再算加减法;
(2)先变形为9.81×0.1+5×9.81+4.9×9.81,再根据乘法分配律计算;
(3)先算小括号里面的加法,再算中括号里面的减法,最后计算括号外面的除法;
(4)先算小括号里面的减法,再计算括号外面的乘除法;
(5)根据加法交换律和减法的性质计算;
(6)根据比例的基本性质计算;
(7)根据等式的性质,先方程两边同时减去35,再两边同时除以5即可求解.
解答:
解:(1)14.85-1.58×8+31.2÷1.2
=14.85-12.64+26
=2.21+26
=28.21
(2)9.81×0.1+0.5×98.1+0.049×981
=9.81×0.1+5×9.81+4.9×9.81
=9.81×(0.1+5+4.9)
=9.81×10
=98.1
(3)[1-(
+
)]÷
=[1-
]÷
=
÷
=9
(4)
×
÷(
-
)
=
×
×
=
(5)75-7.5+25-42
=75+25-(42
+7.5)
=100-50
=50
(6)2:2=x:51
x=2×51÷2
x=51
(7)5x+35=40
5x+35-35=40-35
5x=5
5x÷5=5÷5
x=1
点评:考查了运算定律与简便运算,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简便计算.