Q 12-13-019NEETJEE MainMedium
The half-life of a radioactive substance is $69.3$ days. Its mean life is
Answer: (B) $100$ days
Concept. Mean life $\tau = \dfrac{1}{\lambda} = \dfrac{T_{1/2}}{\ln 2}$.
Step 1. Substitute.
$$\tau = \frac{69.3}{0.693} = 100\ \text{days}$$
Answer. $100$ days (Option B).
Solution by Sreeraj P, M.Sc Physics