§5. Обыкновенные дроби — Упражнения — 5.260 — стр. 45

\(\frac{2}{5} + \frac{1}{5} = \frac{3}{5}\)

\(\frac{3}{5} + \frac{2}{5} = \frac{5}{5} = 1\)

\(1 - \frac{3}{7} = \frac{7}{7} - \frac{3}{7} = \frac{4}{7}\)

\(\frac{4}{7} + \frac{1}{7} = \frac{5}{7}.\)

Ответ: \( \frac{5}{7} \).

\(\frac{5}{17} + \frac{7}{17} = \frac{12}{17}\)

\(\frac{12}{17} - \frac{12}{17} = 0\)

\(0 + \frac{7}{9} = \frac{7}{9}\)

\(\frac{7}{9} - \frac{4}{9} = \frac{3}{9}.\)

Ответ: \( \frac{3}{9} \).

\(2\ \text{га} : 4 = 200\ \text{а} : 4 = 50\ \text{а}\)

\(50\ \text{а} - 20\ \text{а} = 30\ \text{а}\)

\(30\ \text{а} : 15 = 2\ \text{а}\)

\(2\ \text{а} = 200\ \text{м}^2 : 50\ \text{м}^2 = 4\ \text{м}^2.\)

Ответ: \( 4\ \text{м}^2 \).

\(5\ \text{дм}^3 : 100 = 5\ 000\ \text{см}^3 : 100 = 50\ \text{см}^3\)

\(50\ \text{см}^3 - 25\ \text{см}^3 = 25\ \text{см}^3\)

\(25\ \text{см}^3 \cdot 5 = 125\ \text{см}^3\)

\(125\ \text{см}^3 \cdot 8 = 1\ 000\ \text{см}^3 = 1\ \text{дм}^3.\)

Ответ: \( 1\ \text{дм}^3 \).