题目内容

怎样简便就怎样算.
3
5
×18×
5
9

6
7
×
2
5
+
2
5
×
9
7

24×
2
7
×
5
12
×21
39
40
×39
2006×
2004
2005

5
2
×
7
8
+
7
8
×
11
2
(1)
3
5
×18×
5
9

=
3
5
×(18×
5
9

=
3
5
×10
=6;

(2)
6
7
×
2
5
+
2
5
×
9
7

=(
6
7
+
9
7
)×
2
5

=
15
7
×
2
5

=
6
7


(3)24×
2
7
×
5
12
×21
=(21×
2
7
)×(
5
12
×24)
=6×10
=60;

(4)
39
40
×39
=
39
40
×(40-1)
=
39
40
×40-
39
40

=39-
39
40

=38
1
40


(5)2006×
2004
2005

=(2005+1)×
2004
2005

=2005×
2004
2005
+
2004
2005

=2004+
2004
2005

=2004
2004
2005


(6)
5
2
×
7
8
+
7
8
×
11
2

=(
5
2
+
11
2
)×
7
8

=8×
7
8

=7.
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