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简算①925-(337+0.4)②1.8×14+2.2×25%③11×3+13×5+15×7+…+117×19+119×21.

题目详情
简算
①9
2
5
-(3
3
7
+0.4)
②1.8×
1
4
+2.2×25%
1
1×3
+
1
3×5
+
1
5×7
+…+
1
17×19
+
1
19×21
▼优质解答
答案和解析
①9
2
5
-(3
3
7
+0.4),
=9
2
5
-3
3
7
-
2
5

=9
2
5
-
2
5
-3
3
7

=9-3
3
7

=5
4
7


②1.8×
1
4
+2.2×25%,
=1.8×0.25+2.2×0.25,
=(1.8+2.2)×0.25,
=4×0.25,
=1;

1
1×3
+
1
3×5
+
1
5×7
+…+
1
17×19
+
1
19×21

=
1
2
×(1-
1
3
)+
1
2
×(
1
3
-
1
5
)+…+
1
2
×(
1
17
-
1
19
)+
1
2
×(
1
19
-
1
21
),
=
1
2
×(1-
1
3
+
1
3
-
1
5
+…+
1
17
-
1
19
+
1
19
-
1
21
),
=
1
2
×(1-
1
21
),
=
1
2
×
20
21

=
10
21