The half life of the substance is 6.92 days.
Half life can be defined as the time required to reduce the concentration to half of its initial value.
Here the equation given is
[tex]\rm N = N_o e^{-kt}[/tex]
The concentration will reduce to half therefore
[tex]\rm N= \dfrac{N_o}{2}[/tex]
so,
[tex]\rm 39/2 = 39 e^{- 0.1001 * t_{1/2}}[/tex]
ln 0.5 = - 0.1001 * t(1/2)
-0.693 = -.1001 * t(1/2)
t(1/2) = 6.92 days.
Therefore the half life of the substance is 6.92 days.
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