half life: 1620, initial quantity:x, amount after 1000 years:1.5 g
I need to solve for the initial quantity with the info given, thx for the help
we use the equation $\displaystyle I(t) = I_0e^{rt}$
where $\displaystyle r$ is the rate of decay, $\displaystyle I(t)$ is the amount at time $\displaystyle t$, $\displaystyle I_0$ is the intial amount (what we are searching for).
now, $\displaystyle \mbox{half-life} = \frac {\ln 2}r$
you know the half-life, so you can find $\displaystyle r$.
once you have $\displaystyle r$. plug in $\displaystyle I(t) = 1.5$, $\displaystyle t = 1000$, and $\displaystyle r = $ whatever. and solve for $\displaystyle I_0$