[tex] \frac{3}{20} - \frac{1}{40} = \frac{6-1}{40} \frac{5}{40} = \frac{1}{8} [/tex]
[tex] \frac{7}{9} - \frac{1}{36} = \frac{28-1}{36} = \frac{27}{36} = \frac{9}{12} = \frac{3}{4} [/tex]
[tex] \frac{17}{12} - \frac{7}{24} = \frac{34-7}{24} = \frac{27}{24} [/tex]
