问题 解答题
(1)
1
2
+
1
5
=
(2)12×(
1
4
+
1
6
)=
(3)
3
20
×
(6
2
3
×
0.8+6
2
3
×
0.2)=
(4)(
1
15
+
2
17
)×15×17=
(5)
1
1×2
+
1
2×3
+
1
3×4
+…+
1
98×99
+
1
99×100
答案

(1)

1
2
+
1
5

=

5
10
+
2
10

=

7
10

(2)12×(

1
4
+
1
6
),

=12×

1
4
+12×
1
6

=3+2,

=5;

(3)

3
20
×(6
2
3
×
0.8+6
2
3
×
0.2),

=

3
20
×[6
2
3
×
(0.8+0.2)],

=

3
20
×[6
2
3
×
1],

=

3
20
×6
2
3

=1;

(4)(

1
15
+
2
17
)×15×17,

=

1
15
×15×17+
2
17
×15×17,

=17+30,

=47;

(5)

1
1×2
+
1
2×3
+
1
3×4
+…+
1
98×99
+
1
99×100

=(1-

1
2
)+(
1
2
-
1
3
)+(
1
3
-
1
4
)+…+(
1
98
-
1
99
)+(
1
99
-
1
100
),

=1-

1
2
+
1
2
-
1
3
+
1
3
-
1
4
+…+
1
98
-
1
99
+
1
99
-
1
100

=1-

1
100

=

99
100

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