题目内容
(2012?平顺县模拟)计算下列各题.(能简算的要简算)
(1)7.8×
+2.2×20%
(2)0.5×[5
÷﹙
-
﹚]
(3)(198+32×72)-2472÷24
(4)4
×[2.6+
-(0.65+1
)]÷2
.
(1)7.8×
1 |
5 |
(2)0.5×[5
1 |
5 |
7 |
8 |
1 |
16 |
(3)(198+32×72)-2472÷24
(4)4
2 |
5 |
3 |
4 |
3 |
4 |
3 |
4 |
分析:(1)把分数和百分数化成小数,运用乘法分配律的逆运算简算;
(2)先算下括号内的,再算中括号内的,最后算括号外的;
(3)先算括号内的乘法和括号外的2472÷24,得=(198+2304)-103,把198看作200-2,把2304看作2300+4,把103看作100+3,运用加法交换律与结合律简算;
(4)中括号内先去小括号,运用加法交换律与结合律简算,得
×0.95×
,因为0.95能与5约分,不用化成分数,直接约分即可.
(2)先算下括号内的,再算中括号内的,最后算括号外的;
(3)先算括号内的乘法和括号外的2472÷24,得=(198+2304)-103,把198看作200-2,把2304看作2300+4,把103看作100+3,运用加法交换律与结合律简算;
(4)中括号内先去小括号,运用加法交换律与结合律简算,得
22 |
5 |
4 |
11 |
解答:解:(1)7.8×
+2.2×20%,
=7.8×0.2+2.2×0.2,
=(7.8+2.2)×0.2,
=10×0.2,
=2;
(2)0.5×[5
÷﹙
-
﹚],
=0.5×[
÷
],
=0.5×[
×
],
=0.5×
,
=3.2;
(3)(198+32×72)-2472÷24,
=(198+2304)-103,
=[(200-2)+(2300+4)]-103,
=[200+2300+(4-2)]-103,
=2500+2-(100+3),
=2500-100-(3-2),
=2400-1,
=2399;
(4)4
×[2.6+
-(0.65+1
)]÷2
,
=4
×[2.6+
-0.65-1
]÷2
,
=4
×[2.6-0.65-(1
-
)]×
,
=
×[1.95-1]×
,
=
×0.95×
,
=1.52.
1 |
5 |
=7.8×0.2+2.2×0.2,
=(7.8+2.2)×0.2,
=10×0.2,
=2;
(2)0.5×[5
1 |
5 |
7 |
8 |
1 |
16 |
=0.5×[
26 |
5 |
13 |
16 |
=0.5×[
26 |
5 |
16 |
13 |
=0.5×
32 |
5 |
=3.2;
(3)(198+32×72)-2472÷24,
=(198+2304)-103,
=[(200-2)+(2300+4)]-103,
=[200+2300+(4-2)]-103,
=2500+2-(100+3),
=2500-100-(3-2),
=2400-1,
=2399;
(4)4
2 |
5 |
3 |
4 |
3 |
4 |
3 |
4 |
=4
2 |
5 |
3 |
4 |
3 |
4 |
3 |
4 |
=4
2 |
5 |
3 |
4 |
3 |
4 |
4 |
11 |
=
22 |
5 |
4 |
11 |
=
22 |
5 |
4 |
11 |
=1.52.
点评:在脱式计算中,特别注意运算顺序和运算法则,对分数、小数、百分数的互化要细心,根据题目情况,灵活处理.注意运用所学定律,进行简算.
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