Solve the following arithmetic problems: c) (0.5) + (-0.25) + (-0.2); d) (200) ÷ (1/4) ÷ (0.2)

$$0.25 - 0.2 = 0.05$$

The solution is $\boxed{0.05}$.

Dividing by a fraction is equivalent to multiplying by its reciprocal.

$$(200) \div \left(\frac{1}{4}\right) = 200 \times 4 = 800$$

$$800 \div 0.2 = 800 \div \frac{2}{10} = 800 \div \frac{1}{5} = 800 \times 5 = 4000$$

The solution is $\boxed{4000}$.