$\frac{2}{ }=\frac{6}{21}$  

What is the missing number?

 $1\ \frac{2}{3}+3\ \frac{1}{2}-\frac{5}{6}$  

Simplify:

 $\frac{4}{5}-\frac{1}{3}=$  

 $\frac{3}{17}+\frac{5}{17}-\frac{1}{17}=$  

 $\frac{2}{3}\times\frac{1}{5}=$  

 $\frac{2}{7}\times\frac{5}{4}=$  

 $1\ \frac{2}{3}\times3\ \frac{1}{2}=$  

 $\frac{5}{8}\div\frac{15}{16}=$  

 $6\times\frac{2}{3}=$  

 $6\div\frac{2}{3}=$  

 $2\ \frac{1}{2}+\frac{3}{4}\times\frac{1}{6}=$  

 $3\ \frac{1}{3}\div\left(2\frac{3}{4}-2\frac{1}{2}\right)=$