题目内容
用递等式计算,能简算的要简算
(1)43×8-420÷15
(2)
+2
+
+3
(3)
×
÷15
(4)(
+
)÷
-
(5)3.9×9.77+0.23×3.9
(6)
+(
-
)×
.
(1)43×8-420÷15
(2)
3 |
4 |
9 |
17 |
1 |
4 |
8 |
17 |
(3)
8 |
9 |
5 |
16 |
(4)(
1 |
2 |
1 |
3 |
3 |
5 |
17 |
18 |
(5)3.9×9.77+0.23×3.9
(6)
2 |
3 |
4 |
5 |
2 |
3 |
5 |
3 |
分析:(1)先同时运算乘法和除法,再算减法;
(2)运用加法交换律和加法结合律简算;
(3)按照从左到右的顺序计算;
(4)先算小括号里面的加法,再算括号外的除法,最后算减法;
(5)运用乘法分配律简算;
(6)先算小括号里面的减法,再算括号外的乘法,最后算加法.
(2)运用加法交换律和加法结合律简算;
(3)按照从左到右的顺序计算;
(4)先算小括号里面的加法,再算括号外的除法,最后算减法;
(5)运用乘法分配律简算;
(6)先算小括号里面的减法,再算括号外的乘法,最后算加法.
解答:解:(1)43×8-420÷15,
=344-28,
=316;
(2)
+2
+
+3
,
=(
+
)+(3
+2
),
=1+6,
=7;
(3)
×
÷15,
=
×
,
=
;
(4)(
+
)÷
-
,
=
×
-
,
=
-
,
=
;
(5)3.9×9.77+0.23×3.9,( )
=3.9×(9.77+0.23),
=3.9×10,
=39;
(6)
+(
-
)×
,
=
+
×
,
=
+
,
=
.
=344-28,
=316;
(2)
3 |
4 |
9 |
17 |
1 |
4 |
8 |
17 |
=(
3 |
4 |
1 |
4 |
8 |
17 |
9 |
17 |
=1+6,
=7;
(3)
8 |
9 |
5 |
16 |
=
5 |
18 |
1 |
15 |
=
1 |
54 |
(4)(
1 |
2 |
1 |
3 |
3 |
5 |
17 |
18 |
=
5 |
6 |
5 |
3 |
17 |
18 |
=
25 |
18 |
17 |
18 |
=
4 |
9 |
(5)3.9×9.77+0.23×3.9,( )
=3.9×(9.77+0.23),
=3.9×10,
=39;
(6)
2 |
3 |
4 |
5 |
2 |
3 |
5 |
3 |
=
2 |
3 |
2 |
15 |
5 |
3 |
=
2 |
3 |
2 |
9 |
=
8 |
9 |
点评:本题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
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