4) 2-3= 5

Решение:
$$2 \frac{2}{5} \times 3 = \frac{2 \times 5 + 2}{5} \times 3 = \frac{12}{5} \times 3 = \frac{12 \times 3}{5} = \frac{36}{5} = 7 \frac{1}{5}$$

Ответ: $$7 \frac{1}{5}$$