A radio active isotope has a half-life of T years. How long will it take the activity to reduce to
3.125%

Explanation

Here `(N)/(N_(0))=(3.125)/(100)=(1)/(32)`
From `(N)/(N_(0))=((1)/(2))^(n)=(1)/(32)((1)/(2))^(5) therefore n = 5`
From `t = nT = 5T`