1. 用字母表示运算律。
加法交换律：
加法结合律：
乘法交换律：
乘法结合律：
乘法分配律：

​ a+b=b+a​
​ (a+b)+c=a+(b+c)​
​ a×b=b×a​
​ (a×b)×c=a×(b×c)​
​ a×(b+c)=a×b+a×c​

2. 在$□$里填合适的数，使各题能简便计算。
$13.75-(□ +0.27)$ $6.4× 17.4-6.4× □$
$3.94+1.58+□ +□$ $25× 125× □$

0.73
7.4
0.06
0.42
32

3. 判断题。
(1)$12÷ 7.5-1.2÷ 0.75=0$()
(2)$1.2× 0.75-0.75× 1.2=0$()
(3)$1.2× 0.75÷ 1.2÷ 0.75=1$()

(4)$104-104× \frac {5}{8}=0$()

√
√
√
×

4. 下面各题，怎样算简便就怎样算。
$1.9-1.9× (1.9-1.9)$ $1200-197$ $\frac {8}{9}× [\frac {3}{4}-(\frac {7}{16}-\frac {1}{4})]$
$41× 101$ $5.6× 0.99$ $0.7+3.9+4.3+6.1$
$48× (\frac {1}{4}+\frac {1}{6}-\frac {1}{3})$ $97× \frac {1}{9}+2÷ 9$ $(\frac {5}{8}+\frac {3}{19})× 8-\frac {5}{19}$
$95.6× 1.8+0.44× 18$ $2.5× 32× 1.25$ $\frac {5}{19}× \frac {6}{13}+\frac {7}{19}× \frac {5}{13}$
$7.28-\frac {3}{8}+4.72-\frac {5}{8}$ $(3.14× 5+3.14× 3)× 1.25$

=1.9-1.9×0
=1.9
=1200-(200-3)
=1200-200+3
=1003
$​=\frac 89×[\frac 34+\frac 14-\frac 7{16}]​$
$​=\frac 89×\frac 9{16}​$
$​=\frac 12​$
=(0.7+4.3)+(3.9+6.1)
=5+10
=15
=41×(100+1)
=41×100+41×1
=4141
=5.6×(1-0.01)
=5.6×1-5.6×0.01
=5.6-0.056
=5.544
$​=48×\frac 14+48×\frac 16-48×\frac 13​$
​=12+8-16​
​=4​
$​=97×\frac 19+2×\frac 19​$
$​=(97+2)×\frac 19​$
$​=99×\frac 19​$
​=11​
$​=\frac 58×8+\frac 3{19}×8-\frac 5{19}​$
$​=5+(\frac {24}{19}-\frac 5{19})​$
​=5+1​
​=6​
=9.56×18+0.44×18
=(9.56+0.44)×18
=10×18
=180
=2.5×(4×8)×1.25
=(2.5×4)×(8×1.25)
=10×10
=100
$​=\frac 5{19}×\frac 6{13}+\frac 5{19}×\frac 7{13}​$
$​=\frac 5{19}×(\frac 6{13}+\frac 7{13})​$
$​=\frac {5}{19}​$
$​=(7.28+4.72)-(\frac 38+\frac 58)​$
​=12-1​
​ =11​
=3.14×(5+3)×1.25
=3.14×(8×1.25)
=3.14×10
=31.4