题目内容
脱式计算(能简算的要简算)
(1)
÷[1÷(
-
)]
(2)3.6-2.8+7.4-7.2
(3)87×
+
.
(1)
1 |
6 |
3 |
5 |
3 |
10 |
(2)3.6-2.8+7.4-7.2
(3)87×
3 |
86 |
83 |
86 |
分析:(1)先算小括号里面的减法,再算中括号里面的除法,最后算括号外的除法.
(2)运用加法结合律简算;
(3)先把87看成86+1,再运用乘法分配律简算;然后再运用加法结合律简算.
(2)运用加法结合律简算;
(3)先把87看成86+1,再运用乘法分配律简算;然后再运用加法结合律简算.
解答:解:(1)
÷[1÷(
-
)],
=
÷[1÷
],
=
÷
,
=
;
(2)3.6-2.8+7.4-7.2,
=(3.6+7.4)-(2.8+7.2),
=11-10,
=1;
(3)87×
+
,
=(86+1)×
+
,
=86×
+1×
+
,
=3+
+
,
=3+(
+
),
=3+1,
=4.
1 |
6 |
3 |
5 |
3 |
10 |
=
1 |
6 |
3 |
10 |
=
1 |
6 |
10 |
3 |
=
1 |
20 |
(2)3.6-2.8+7.4-7.2,
=(3.6+7.4)-(2.8+7.2),
=11-10,
=1;
(3)87×
3 |
86 |
83 |
86 |
=(86+1)×
3 |
86 |
83 |
86 |
=86×
3 |
86 |
3 |
86 |
83 |
86 |
=3+
3 |
86 |
83 |
86 |
=3+(
3 |
86 |
83 |
86 |
=3+1,
=4.
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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