$\frac{4\ast 3}{27\ast 8}=\frac{\stackrel{1}{\bcancel{4}}\ast \stackrel{1}{\bcancel{3}}}{\underset{9}{\bcancel{27}}\ast \underset{2}{\bcancel{8}}}=\frac{1}{18}$

$\frac{12\ast 14}{35\ast 15}=\frac{\stackrel{4}{\bcancel{12}}\ast \stackrel{2}{\bcancel{14}}}{\underset{5}{\bcancel{35}}\ast \underset{5}{\bcancel{15}}}=\frac{8}{25}$

$\frac{17\ast 22}{55\ast 34}=\frac{\stackrel{1}{\bcancel{17}}\ast \stackrel{2}{\bcancel{22}}}{\underset{5}{\bcancel{55}}\ast \underset{2}{\bcancel{34}}}=\frac{2}{10}=\frac{1}{5}$

$\frac{12\ast 14}{35\ast 15}=\frac{\stackrel{4}{\bcancel{12}}\ast \stackrel{2}{\bcancel{14}}}{\underset{5}{\bcancel{35}}\ast \underset{5}{\bcancel{15}}}=\frac{8}{25}$

$\frac{8\ast 13\ast 45}{15\ast 24\ast 39}=\frac{\stackrel{1}{\bcancel{8}}\ast \stackrel{1}{\bcancel{13}}\ast \stackrel{3}{\bcancel{45}}}{\underset{1}{\bcancel{15}}\ast \underset{3}{\bcancel{24}}\ast \underset{3}{\bcancel{39}}}=\frac{3}{9}=\frac{1}{3}$

$\frac{9\ast 14+9\ast 5}{18\ast 38}=\frac{9\ast (14+5)}{18\ast 38}=\frac{9\ast 19}{18\ast 38}=\frac{\stackrel{1}{\bcancel{9}}\ast \stackrel{1}{\bcancel{19}}}{\underset{2}{\bcancel{18}}\ast \underset{2}{\bcancel{38}}}=\frac{1}{4}$

$\frac{15\ast 21}{15\ast 32-15\ast 4}=\frac{15\ast 21}{15\ast (32-4)}=\frac{15\ast 21}{15\ast 28}=\frac{\stackrel{1}{\bcancel{15}}\ast \stackrel{3}{\bcancel{21}}}{\underset{1}{\bcancel{15}}\ast \underset{4}{\bcancel{28}}}=\frac{3}{4}$

$\frac{42\ast 17-16\ast 17}{51\ast 7+51\ast 6}=\frac{17\ast (42-16)}{51\ast (7+6)}=\frac{17\ast 26}{51\ast 13}=\frac{\stackrel{1}{\bcancel{17}}\ast \stackrel{2}{\bcancel{26}}}{\underset{3}{\bcancel{51}}\ast \underset{1}{\bcancel{13}}}=\frac{2}{3}$