题目内容

计算下列各题,能简便都尽量简便.
(1)(
3
4
-
1
8
5
12

(2)[1-(
3
5
-
1
4
)]÷13
(3)3.75×4.8+62.5×0.48 (4)
4
15
÷(
4
7
+
4
8
(5)1991+199.1+19.91+1.991 (6)
44
45
×37.
分析:(1)先把除法变成乘法,再运用乘法分配律简算;
(2)先算小括号里面的减法,再算中括号里面的减法,最后算括号外的除法;
(3)先把62.5×0.48根据积不变规律变成6.25×4.8,再运用乘法分配律简算;
(4)先算小括号里面的加法,再算括号外的除法;
(5)运用凑整法简算;
(6)把
44
45
分解成1-
1
45
,再运用乘法分配律简算.
解答:解:(1)(
3
4
-
1
8
5
12

=(
3
4
-
1
8
)×
12
5

=
3
4
×
12
5
-
1
8
×
12
5

=
9
5
-
3
10

=
3
2


(2)[1-(
3
5
-
1
4
)]÷13

=[1-
7
20
]÷13,
=
13
20
÷13,
=
1
20


(3)3.75×4.8+62.5×0.48,
=3.75×4.8+6.25×4.8,
=(3.75+6.25)×4.8,
=10×4.8,
=48;

(4)
4
15
÷(
4
7
+
4
8
),
=
4
15
÷
15
14

=
56
225


(5)1991+199.1+19.91+1.991,
=(2000-9)+(200-0.9)+(20-0.09)+(2-0.009),
=(2000+200+20+2)-(9+0.9+0.09+0.009),
=2222-9.999,
=2222-(10-0.001),
=2222-10+0.001,
=2212.001;

(6)
44
45
×37,
=(1-
1
45
)×37,
=1×37-
1
45
×37,
=37-
37
45

=36
8
45
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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