## Calculus (3rd Edition)

The decay constant is $4.27\times 10^{-4}$.
The half-life is given by $$\frac{\ln 2}{k}\Longrightarrow 1622= \frac{\ln 2}{k}\Longrightarrow k= \frac{\ln 2}{1622}=4.27\times 10^{-4}.$$ So the decay constant is $4.27\times 10^{-4}$.