d
\(\frac{N}{{{N_0}}}\,\, = \,\,\,{\left( {\frac{1}{2}} \right)^{t/T}}\,\,\,\,\,\, \)

\(\Rightarrow \,\,\,\,{\left( {\frac{1}{2}} \right)^{t/22}} = \,\,\frac{{10}}{{100}}\)

અથવા  \(\,10\,\, = \,\,\,{2^{t\,/22}}\)  અથવા \({\log _{10}}10\,\, = \,\,\frac{t}{{22}}\,\,{\log _{10}}2\)

\(t\,\, = \,\,\frac{{22{{\log }_{10}}10}}{{{{\log }_{10}}2}}\,\, = \,\,\frac{{22\,\, \times \,\,1}}{{0.3010}}\,\, \approx \,\,73\,\,years\)