\[\boxed{\mathbf{211.}}\]
\[\textbf{а)}\ P(A) = \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4}.\]
\[\textbf{б)}\ P(A) = \left( \frac{1}{2} \right)^{4} = \frac{1}{16}.\]
\[\textbf{в)}\ P(A) = \frac{1}{2^{3}} + \frac{1}{2^{4}} = \frac{1}{8} + \frac{1}{16} =\]
\[= \frac{2}{16} + \frac{1}{16} = \frac{3}{16}.\]
\[\textbf{г)}\ P(A) = \left( \frac{1}{2} \right)^{4} = \frac{1}{16}.\]