怎樣算合理簡(jiǎn)便怎樣算
(1)(
2
3
+
1
5
)+(
2
3
-
12
17
)-(
1
5
+
5
17

(2)[5.6-(1.8-
1
5
÷3.7)]×
7
8

(3)75%×
7
17
+
3
4
×
9
17
-
16
17
×0.25
(4)42×(
1
8
+
1
24
+
1
48
+
1
80
+
1
120
+
1
168
分析:(1)利用減法的性質(zhì)與加法結(jié)合律與交換律,把同分母分?jǐn)?shù)先加減;
(2)先算小括號(hào)里面的除,再算減法,再算中括號(hào)里面的減法,最后算乘,注意把小數(shù)化為分?jǐn)?shù)計(jì)算;
(3)先利用乘法分配律簡(jiǎn)算75%×
7
17
+
3
4
×
9
17
=0.75×
16
17
,再進(jìn)一步利用乘法分配律簡(jiǎn)算即可;
(4)把括號(hào)內(nèi)的分?jǐn)?shù)拆分,
1
8
=
1
2
×(
1
2
-
1
4
),
1
24
=
1
2
×(
1
4
-
1
6
)…以此類推,再用乘法分配律展開簡(jiǎn)算即可.
解答:解:(1)(
2
3
+
1
5
)+(
2
3
-
12
17
)-(
1
5
+
5
17

=
2
3
+
1
5
+
2
3
-
12
17
-
1
5
-
5
17

=
2
3
+
2
3
+
1
5
-
1
5
-
12
17
-
5
17

=
4
3
+0-1
=
1
3


(2)[5.6-(1.8-
1
5
÷3.7)]×
7
8

=[5.6-(1.8-
1
5
×
10
37
)]×
7
8

=[5.6-(1.8-
2
37
)]×
7
8

=[3.8+
2
37
7
8

=
713
185
×
7
8

=
4991
1480


(3)75%×
7
17
+
3
4
×
9
17
-
16
17
×0.25
=75%×(
7
17
+
9
17
)-
16
17
×0.25
=75%×
16
17
-
16
17
×0.25
=(75%-0.25)×
16
17

=
1
2
×
16
17

=
8
17


(4)42×(
1
8
+
1
24
+
1
48
+
1
80
+
1
120
+
1
168

=42×
1
2
×(
1
2
-
1
4
+
1
4
-
1
6
+
1
6
-
1
8
+
1
8
-
1
10
+
1
10
-
1
12
+
1
12
-
1
14

=42×
1
2
×(
1
2
-
1
14

=42×
1
2
×
1
2
-42×
1
2
×
1
14

=
21
2
-
3
2

=9.
點(diǎn)評(píng):抓住數(shù)字和運(yùn)算符號(hào)的特點(diǎn),靈活運(yùn)用運(yùn)算定律進(jìn)行簡(jiǎn)算,小數(shù)和分?jǐn)?shù)的混合運(yùn)算注意能化成有限小數(shù)的化為小數(shù)計(jì)算,否則化為分?jǐn)?shù)計(jì)算.
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