science
posted by Prince .
If the half life period of a radioactive element is 1600.After how many years will if remains 25% of his quantity

1600 what? If it isn't years, convert to years.
k = 0.693/t_{1/2}
Substitute k into the below equation.
ln(No/N) = kt
No = 100
N = 25
k from above
Solve for t in years.
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