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  4. After 150 days, the activity of a radioactive sample is 5000 dps. The activity becomes 2500 dps after another 75 days. The initial activity of the sample is

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Q. After $150$ days, the activity of a radioactive sample is $5000$ dps. The activity becomes $2500 $ dps after another $75 $ days. The initial activity of the sample is

Nuclei

Solution:

Activity of sample becomes $2500$ from $5000$ in $75$ days therefore its half life is $75$ days, so
$R =\frac{ R _0}{2^{\frac{150}{75}}}=5000$
$ \Rightarrow R _0=5000 \times 4=20,000$