74，83

16，65

28，91

21，52

24，43

70，105

66，65

92，137

$$\frac{8}{11}$$  

$$\frac{11}{13}$$  

$$\frac{10}{11}$$  

$$\frac{11}{12}$$  

$$\frac{A}{B}\div\frac{C}{D}\ =\ \frac{A}{B}\times\frac{D}{C}$$  

$$\frac{A}{B}\div C\ =\ \frac{A}{B}\times\frac{1}{C}$$

$$\frac{A}{B}\div\frac{C}{D}\ =\ \frac{B}{A}\times\frac{D}{C}$$  

$$A\div B\ =\ \frac{A}{B}$$

$$\frac{A}{B}\div C\ =\ \frac{A}{B}\times\frac{1}{C}$$

$$45\frac{1}{2}\div1\frac{4}{5}-100$$  

$$100-45\frac{1}{2}\div1\frac{4}{5}$$  

$$45\frac{1}{2}\times1\frac{4}{5}-100$$  

$$100-45\frac{1}{2}\times1\frac{4}{5}$$