A radioactive sample is undergoing α decay. At any time t1, its activity is A and another time t2, the activity is \(\frac{A}{5}\). What is the average life time for the sample?
1
\(\frac{{ln5}}{{{t_2} - {t_1}}}\)
2
\(\frac{{ln({t_2} + {t_1})}}{2}\)
3
\(\frac{{{t_2} - {t_1}}}{{ln5}}\)
4
\(\frac{{{t_1} - {t_2}}}{{ln5}}\)