[tex]\displaystyle a)6 \frac{2}{7} -4 \frac{1}{7} = \frac{6 \cdot 7+2}{7} - \frac{4 \cdot 7+1}{7} = \frac{42+2}{7} - \frac{28+1}{7} = \frac{44}{7} - \frac{29}{7} = \frac{15}{7} \\ \\ b)12 \frac{1}{9} -5 \frac{4}{9} = \frac{12 \cdot 9+1}{9} - \frac{5 \cdot 9+4}{9} = \frac{108+1}{9} - \frac{45+4}{9} = \\ \\ = \frac{109}{9} - \frac{49}{9} = \frac{60}{9} = \frac{20}{3} [/tex]
[tex]\displaystyle c)8 \frac{4}{5} -3 \frac{1}{5} = \frac{8 \cdot 5+4}{5} - \frac{3 \cdot 5+1}{5} = \frac{40+4}{5} - \frac{15+1}{5} = \frac{44}{5} - \frac{16}{5} = \frac{28}{5} \\ \\ d)18 \frac{2}{11} -7 \frac{5}{11} = \frac{18 \cdot 11+2}{11} - \frac{7 \cdot 11+5}{11} = \frac{198+2}{11} - \frac{77+5}{11} = \\ \\ = \frac{200}{11} - \frac{82}{11} = \frac{118}{11} [/tex]
