题目内容

计算下面各题,怎样简便就怎样算
5
9
×(
9
5
+18)
4
5
-
4
5
÷4
1
2
×
3
5
+
2
5
×
1
2
1
7
×
5
13
+
8
13
÷7
19-19×
99
100
7
8
-
4
9
×
3
8
分析:(1)(3)(5)运用乘法分配律简算;
(2)同时运算除法,再算减法;
(4)先把除法变成乘法,再运用乘法分配律简算;
(6)先算乘法,再算减法.
解答:解:(1)
5
9
×(
9
5
+18),
=
5
9
×
9
5
+
5
9
×18,
=1+10,
=11;

(2)4÷
4
5
-
4
5
÷4,
=5-
1
5

=4
4
5


(3)
1
2
×
3
5
+
2
5
×
1
2

=
1
2
×(
3
5
+
2
5
),
=
1
2
×1,
=
1
2


(4)
1
7
×
5
13
+
8
13
÷7,
=
1
7
×
5
13
+
8
13
×
1
7

=
1
7
×(
5
13
+
8
13
),
=
1
7
×1,
=
1
7


(5)19-19×
99
100

=19×(1-
99
100
),
=19×
1
100

=
19
100


(6)
7
8
-
4
9
×
3
8

=
7
8
-
4
24

=
17
24
点评:本题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
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