178. The half-life of polonium-A is 8 years. What percentage of this material remains after 32 years? (1) $16\%$ (2) $24\%$ (3) $32\%$ (4) $64\%$
\textbf{178.} The half-life of polonium-A is 8 years. What percentage of this material remains after 32 years?
(1) $16\%$ \quad (2) $24\%$ \quad (3) $32\%$ \quad (4) $64\%$