题目内容

脱式计算:
(1)0.25×〔
7
20
÷(4-2.4×
5
6
)〕
(2)〔1
4
9
-8.19÷(5.25+1
3
4
)〕×
9
13
÷17%
(3)6
7
13
-(5
3
7
-1
7
13
)+1
4
7
           
(4)4.83×0.59+0.41×1.59-0.324×5.9
(5)5.6-(□×3
1
4
-1
5
6
×□)÷5
2
3
=2
3
5
,□=
12
12
分析:(1)、(2)、(3)按整数、分数、小数、百分数四则混合运算的运算顺序和计算法则进行计算;
(4)把0.324×5.9变成3.24×0.59后先运用乘法分配律计算4.83×0.59-3.24×0.59,得到1.59×0.59,然后再运用乘法分配律进行简算;
(5)“□”为未知数,用解方程的解题思路求解.
解答:解:(1)0.25×〔
7
20
÷(4-2.4×
5
6
)〕,
=0.25×〔
7
20
÷(4-
12
5
×
5
6
)〕,
=0.25×〔
7
20
÷(4-2)〕,
=0.25×〔
7
20
÷2〕,
=
1
4
×
7
40

=
7
160


(2)〔1
4
9
-8.19÷(5.25+1
3
4
)〕×
9
13
÷17%,
=〔1
4
9
-8.19÷(5.25+1.75)〕×
9
13
÷17%,
=〔1
4
9
-8.19÷7〕×
9
13
÷17%,
=〔1
4
9
-1.17〕×
9
13
×
100
17

=(
4
9
-
17
100
)×
9
13
×
100
17

=
4
9
×
9
13
×
100
17
-
17
100
×
9
13
×
100
17

=
400
221
-
9
13

=
400
221
-
153
221

=
247
221


(3)6
7
13
-(5
3
7
-1
7
13
)+1
4
7

=6
7
13
-5
3
7
+1
7
13
+1
4
7

=6
49
91
-5
39
91
+1
49
91
+1
52
91

=1
10
91
+1
49
91
+1
52
91

=4
7
13


(4)4.83×0.59+0.41×1.59-0.324×5.9,
=4.83×0.59+0.41×1.59-3.24×0.59,
=(4.83-3.24)×0.59+0.41×1.59,
=1.59×0.59+0.41×1.59,
=(0.59+0.41)×1.59,
=1×1.59,
=1.59;

(5)5.6-(□×3
1
4
-1
5
6
×□)÷5
2
3
=2
3
5

            5.6-(
17
12
×□)÷5
2
3
=2
3
5

            5.6-(
17
12
×□)×
3
17
=2
3
5

                      5.6-
1
4
×□=2
3
5

                         
1
4
×□=5.6-2.6,
□=3÷
1
4

□=12.
故答案为:(1)
7
160
;(2)
247
221
;(3)4
7
13
;(4)1.59;(5)12.
点评:此题考查整数、分数、小数、百分数四则混合运算,按计算法则计算,同时注意运用定律进行简算.
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