[tex]m=0,25m_{0}\\
t=\?\\
\tau_{\frac{1}{2}}=45,1d\\\\
0,25m_{0}=m_{0}*({\frac{1}{2})^{\frac{t}{45,1}}}\\\\
0,25=\frac{1}{2}^{\frac{t}{45,1}}\\\\
log_{a}{b}=c \ \ \Leftrightarrow \ \ a^{c}=b\\\\
\frac{t}{45,1}=log_{\frac{1}{2}}0,25\\\\
\frac{t}{45,1}=2\\\\
t=90,2d[/tex]
