2) 8 5/12 - 6 7/20 4) 9 17/24 - 8 11/36

Решение:

1. 2) 8 5/12 - 6 7/20
   \[ 8 \frac{5}{12} - 6 \frac{7}{20} = (8-6) + (\frac{5}{12} - \frac{7}{20}) = 2 + \frac{25-21}{60} = 2 + \frac{4}{60} = 2 + \frac{1}{15} = 2 \frac{1}{15} \]
2. 4) 9 17/24 - 8 11/36
   \[ 9 \frac{17}{24} - 8 \frac{11}{36} = (9-8) + (\frac{17}{24} - \frac{11}{36}) = 1 + \frac{51-22}{72} = 1 + \frac{29}{72} = 1 \frac{29}{72} \]

Ответ: 2) 2 1/15; 4) 1 29/72