题目内容
用递等式计算(能简便的要简便计算) 2.98×103-2.98×3; |
|
2
| ||||||||||||
|
15.12÷4×2.5; |
| ||||||||||||
22.78-22.78÷3.4; |
|
分析:(1)运用乘法分配律的逆运算简算;
(2)运用加法交换律与结合律简算;
(3)运用减法的性质简算;
(4)通分计算即可;
(5)按运算顺序从左向右依次计算;
(6)运用加法的性质,去括号简算;
(7)按运算顺序计算,先算除法,再算减法;
(8)运用运用加法交换律与结合律简算.
(2)运用加法交换律与结合律简算;
(3)运用减法的性质简算;
(4)通分计算即可;
(5)按运算顺序从左向右依次计算;
(6)运用加法的性质,去括号简算;
(7)按运算顺序计算,先算除法,再算减法;
(8)运用运用加法交换律与结合律简算.
解答:解:(1)2.98×103-2.98×3,
=(103-3)×2.98,
=100×2.98,
=298;
(2)
-
+
,
=(
+
)-
,
=1-
,
=
;
(3)2
-
-
,
=2
-(
+
),
=2
-1,
=1
;
(4)
+
-
,
=
+
-
,
=
;
(5)15.12÷4×2.5,
=3.78×2.5,
=9.45;
(6)
-(
+
),
=
-
-
,
=
-
,
=
;
(7)22.78-22.78÷3.4,
=22.78-6.7,
=16.08;
(8)
+
+
+
,
=(
+
)+(
+
),
=1+1
,
=2
.
=(103-3)×2.98,
=100×2.98,
=298;
(2)
11 |
15 |
3 |
7 |
4 |
15 |
=(
11 |
15 |
4 |
15 |
3 |
7 |
=1-
3 |
7 |
=
4 |
7 |
(3)2
1 |
3 |
4 |
7 |
3 |
7 |
=2
1 |
3 |
4 |
7 |
3 |
7 |
=2
1 |
3 |
=1
1 |
3 |
(4)
3 |
4 |
5 |
6 |
5 |
8 |
=
18 |
24 |
20 |
24 |
15 |
24 |
=
23 |
24 |
(5)15.12÷4×2.5,
=3.78×2.5,
=9.45;
(6)
7 |
8 |
3 |
8 |
1 |
6 |
=
7 |
8 |
3 |
8 |
1 |
6 |
=
1 |
2 |
1 |
6 |
=
1 |
3 |
(7)22.78-22.78÷3.4,
=22.78-6.7,
=16.08;
(8)
1 |
7 |
3 |
8 |
6 |
7 |
6 |
7 |
=(
1 |
7 |
6 |
7 |
3 |
8 |
6 |
7 |
=1+1
13 |
56 |
=2
13 |
56 |
点评:此题是考查四则混合运算,要仔细观察算式的特点,灵活运用一些定律进行简便计算.
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