Решение:

a) $$20\frac{17}{37} + 14\frac{12}{37} + 31\frac{8}{37} = (20+14+31) + (\frac{17}{37} + \frac{12}{37} + \frac{8}{37}) = 65 + \frac{17+12+8}{37} = 65 + \frac{37}{37} = 65 + 1 = 66$$

б) $$150 - \frac{149}{150} = \frac{150 * 150}{150} - \frac{149}{150} = \frac{22500 - 149}{150} = \frac{22351}{150} = 149\frac{1}{150}$$

в) $$\frac{5}{6} - \frac{3}{8} = \frac{5*4}{6*4} - \frac{3*3}{8*3} = \frac{20}{24} - \frac{9}{24} = \frac{20-9}{24} = \frac{11}{24}$$

г) $$\frac{7}{12} : \frac{8}{9} = \frac{7}{12} * \frac{9}{8} = \frac{7*9}{12*8} = \frac{7*3}{4*8} = \frac{21}{32}$$