脫式計(jì)算
(1)49×
3
7
×
1
3
(2)
1
12
×12
(3)36×(
1
4
+
5
18
(4)10.5÷10.5×
7
10
(5)(1+
3
4
)÷(1-
3
4
(6)2.5×3
1
3
×0.4×
3
10
(7)
7
10
×
5
16
÷
21
32
(8)(
7
10
-
7
10
×
2
7
)÷
1
4
(9)1.4×3.7+3.7×8.6.
分析:(1)根據(jù)乘法結(jié)合律進(jìn)行簡(jiǎn)算;
(2)直接約分進(jìn)行計(jì)算;
(3)根據(jù)乘法分配律進(jìn)行簡(jiǎn)算;
(4)先算除法,再算乘法;
(5)先算加法和減法,再算除法;
(6)根據(jù)乘法交換律和結(jié)合律進(jìn)行簡(jiǎn)算;
(7)先算乘法,再算除法;
(8)先算乘法,再算減法,最后算除法;
(9)根據(jù)乘法分配律進(jìn)行簡(jiǎn)算.
解答:解:
(1)49×
3
7
×
1
3
,
=49×(
3
7
×
1
3
),
=49×
1
7
,
=7;

(2)
1
12
×12=1;

(3)36×(
1
4
+
5
18
),
=36×
1
4
+36×
5
18
,
=9+10,
=19;

(4)10.5÷10.5×
7
10
,
=1×
7
10
,
=
7
10
;

(5)(1+
3
4
)÷(1-
3
4
),
=1
3
4
÷
1
4
,
=7;

(6)2.5×3
1
3
×0.4×
3
10
,
=(2.5×0.4)×(3
1
3
×
3
10
),
=1×1,
=1;

(7)
7
10
×
5
16
÷
21
32
,
=
7
32
÷
21
32

=
1
3
;

(8)(
7
10
-
7
10
×
2
7
)÷
1
4
,
=(
7
10
-
1
5
)÷
1
4
,
=
1
2
÷
1
4

=2;

(9)1.4×3.7+3.7×8.6,
=(1.4+8.6)×3.7,
=10×3.7,
=37.
點(diǎn)評(píng):考查了運(yùn)算定律與簡(jiǎn)便運(yùn)算,四則混合運(yùn)算.注意運(yùn)算順序和運(yùn)算法則,靈活運(yùn)用所學(xué)的運(yùn)算律簡(jiǎn)便計(jì)算.
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