[tex] \frac{1}{20} : ( - \frac{1}{10}) - ( - \frac{3}{5}) = \frac{1}{20} : - \frac{1}{10} - ( - \frac{3}{5}) = \frac{1}{20} \times \frac{10}{ - 1} - ( - \frac{3}{5}) = \frac{1 \times 10}{ - 20} - ( - \frac{3}{5}) = \frac{10}{ - 20} - ( - \frac{3}{5}) = - \frac{10}{20} - ( - \frac{3}{5}) = - \frac{1}{2} - ( - \frac{3}{5}) = - \frac{1}{2} + \frac{3}{5} = \frac{1}{10} [/tex]
