Radioactivity is

The mean life of a radioactive sample are $30\,year$ and $60\,year$ for $\alpha -$ emission and $\beta -$ emission respectively. If the sample decays both by $\alpha -$ emission and $\beta -$ emission simultaneously, then the time after which, only one-fourth of the sample remain is approximately ............ $years$

The half-life of $B{i^{210}}$ is $5\, days$. What time is taken by $(7/8)^{th}$ part of the sample to decay.........$days$

Half life of radioactive element is $12.5\; Hour$ and its quantity is $256\; gm$. After how much time (in $Hours$) its quantity will remain $1 \;gm$

A certain radioactive nuclide of mass number $m_x$ disintegrates, with the emission of an electron and $\gamma$ radiation only, to give second nuclied of mass number $m_y.$ Which one of the following equation correctly relates $m_x$ and $m_y$ ?

Some nuclei of a radioactive material are undergoing radioactive decay. The time gap between the instances when a quarter of the nuclei have decayed and when half of the nuclei have decayed is given as:

(where $\lambda$ is the decay constant)