题目内容

2
9
×
3
5
+
2
9
×
7
5
;                      
4
5
÷[(
5
8
-
1
2
)×
5
8
];
1
8
×58+
1
8
×41+
1
8
;    
13.96÷
5
3
÷6;       
76×
23
73
;                      
24×(
1
6
+
3
8
+
7
12
).
分析:(1)(3)(6)运用乘法分配律简算;
(2)先算小括号里面的减法,再算中括号里面的乘法,最后算括号外的除法;
(4)根据连续除以两个数等于除以这两个数的积来简算;
(5)把76分解成73+3,然后再用乘法分配律简算.
解答:解:(1)
2
9
×
3
5
+
2
9
×
7
5

=
2
9
×(
3
5
+
7
5
),
=
2
9
×2,
=
4
9


(2)
4
5
÷[(
5
8
-
1
2
)×
5
8
],
=
4
5
÷[
1
8
×
5
8
],
=
4
5
÷
5
64

=
256
25


(3)
1
8
×58+
1
8
×41+
1
8

=
1
8
×(58+41+1),
=0.125×100,
=12.5;

(4)13.96÷
5
3
÷6,
=13.96÷(
5
3
×6),
=13.96÷10,
=1.396;

(5)76×
23
73

=(73+3)×
23
73

=73×
23
73
+3×
23
73

=23+
69
73

=23
69
73


(6)24×(
1
6
+
3
8
+
7
12
),
=24×
1
6
+24×
3
8
+24×
7
12

=4+9+14,
=13+14,
=27.
点评:乘法分配律是常用的简便运算的方法,要熟练掌握,灵活运用.
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