3. Решите уравнения: а) 19/20 - (y + 3/10) = 1/20; б) 1,2x + 20,7 = 25,5.

Решение:

1. \( \frac{19}{20} - \left( y + \frac{3}{10} \right) = \frac{1}{20} \)
   \( y + \frac{3}{10} = \frac{19}{20} - \frac{1}{20} \)
   \( y + \frac{3}{10} = \frac{18}{20} \)
   \( y + \frac{3}{10} = \frac{9}{10} \)
   \( y = \frac{9}{10} - \frac{3}{10} \)
   \( y = \frac{6}{10} \)
   \( y = \frac{3}{5} \)
2. \( 1.2x + 20.7 = 25.5 \)
   \( 1.2x = 25.5 - 20.7 \)
   \( 1.2x = 4.8 \)
   \( x = \frac{4.8}{1.2} \)
   \( x = 4 \)

Ответ: а) \( y = \frac{3}{5} \); б) \( x = 4 \).