2) 7 9/20 - 5 17/30 4) 8 5/36 - 1 43/108

Решение:

1. 2) 7 9/20 - 5 17/30
   \[ 7 \frac{9}{20} - 5 \frac{17}{30} = (7-5) + (\frac{9}{20} - \frac{17}{30}) = 2 + \frac{27-34}{60} = 2 - \frac{7}{60} = 1 + \frac{60}{60} - \frac{7}{60} = 1 \frac{53}{60} \]
2. 4) 8 5/36 - 1 43/108
   \[ 8 \frac{5}{36} - 1 \frac{43}{108} = (8-1) + (\frac{5}{36} - \frac{43}{108}) = 7 + \frac{15-43}{108} = 7 - \frac{28}{108} = 7 - \frac{7}{27} = 6 + \frac{27}{27} - \frac{7}{27} = 6 \frac{20}{27} \]

Ответ: 2) 1 53/60; 4) 6 20/27