题目内容
计算:(能用简便方法的用简便方法算法)
420×(
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考点:分数的简便计算
专题:运算定律及简算
分析:(1)(2)(3)运用乘法分配律简算;
(4)先把除法变成乘法,再约分求解;
(5)(6)先把除法变成乘法,再根据乘法结合律简算.
(4)先把除法变成乘法,再约分求解;
(5)(6)先把除法变成乘法,再根据乘法结合律简算.
解答:
解:(1)420×(
+
)
=420×
+420×
=180+350
=530;
(2)
×99+
=
×(99+1)
=
×100
=16;
(3)
×7+
×11
=
×(7+11)
=
×18
=10;
(4)
×
÷
=
×
×3
=5;
(5)
÷
×
=
×
×
=
×(
×
)
=
×
=
;
(6)
÷
×
÷
=
×
×
×
=(
×
)×(
×
)
=
×
=
.
3 |
7 |
5 |
6 |
=420×
3 |
7 |
5 |
6 |
=180+350
=530;
(2)
4 |
25 |
4 |
25 |
=
4 |
25 |
=
4 |
25 |
=16;
(3)
5 |
9 |
5 |
9 |
=
5 |
9 |
=
5 |
9 |
=10;
(4)
7 |
3 |
5 |
7 |
1 |
3 |
=
7 |
3 |
5 |
7 |
=5;
(5)
2 |
3 |
15 |
28 |
5 |
21 |
=
2 |
3 |
28 |
15 |
5 |
21 |
=
2 |
3 |
28 |
15 |
5 |
21 |
=
2 |
3 |
4 |
9 |
=
8 |
27 |
(6)
7 |
21 |
5 |
6 |
9 |
22 |
9 |
11 |
=
7 |
21 |
6 |
5 |
9 |
22 |
11 |
9 |
=(
7 |
21 |
6 |
5 |
9 |
22 |
11 |
9 |
=
2 |
5 |
1 |
2 |
=
1 |
5 |
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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