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①30%×2.84+22125×1.7+2.84×1.5②13+18+115+…+1120③(114+523+334+913)×(2-720)

题目详情
①30%×2.84+2
21
25
×1.7+2.84×1.5
1
3
+
1
8
+
1
15
+…+
1
120

③(1
1
4
+5
2
3
+3
3
4
+9
1
3
)×(2-
7
20
▼优质解答
答案和解析
①30%×2.84+2
21
25
×1.7+2.84×1.5,
=0.3×2.84+2.84×1.7+2.84×1.5,
=2.84×(0.3+1.7+1.5),
=2.84×3.5,
=9.94;

1
3
+
1
8
+
1
15
+…+
1
120

=
1
1×3
+
1
2×4
+
1
3×5
+…+
1
10×12

=
1
2
×[(1-
1
3
)+(
1
2
-
1
4
)+(
1
3
-
1
5
)+…+(
1
10
-
1
12
)],
=
1
2
×(1+
1
2
-
1
11
-
1
12
),
=
1
2
×
175
132

=
175
264


③(1
1
4
+5
2
3
+3
3
4
+9
1
3
)×(2-
7
20
),
=[(1
1
4
+
作业帮用户 2016-12-11