a) $$20 \frac{17}{37}+14\frac{12}{37}+31\frac{8}{37} = (20+14+31) + (\frac{17}{37}+\frac{12}{37}+\frac{8}{37})=65+\frac{17+12+8}{37} = 65+\frac{37}{37}=65+1=66$$
Ответ: 66
б) $$150-\frac{149}{150} = \frac{150*150-149}{150} = \frac{22500-149}{150} = \frac{22351}{150} = 149\frac{1}{150}$$
Ответ: $$149\frac{1}{150}$$
в) $$6\frac{5}{8} = \frac{6*8+5}{8} = \frac{48+5}{8} = \frac{53}{8} = 6,625$$
Ответ: $$6,625$$
г) $$12\frac{7}{9} = \frac{12*9+7}{9} = \frac{108+7}{9} = \frac{115}{9} = 12,777...$$
Ответ: $$12,777...$$