Q 12-13-026JEE MainMedium
A radioactive isotope has a half-life of $5$ years. Find the percentage of the original sample that remains after $15$ years.
Numerical value type. Enter your answer.
Answer: 12.5
Concept. The fraction left is $\left(\dfrac12\right)^{t/T_{1/2}}$.
Step 1. Number of half-lives. $\dfrac{15}{5} = 3$.
Step 2. Fraction left. $\left(\dfrac12\right)^3 = \dfrac18 = 12.5\%$.
Answer. $12.5$.
Solution by Sreeraj P, M.Sc Physics