Answer
a) $N(t)=320\cdot2^t$.
b) $81,920$ mice.
Work Step by Step
a) We are looking for an exponential model in the form $N(t)=Ab^t$, where $t$ is the amount of years passed. At $t=0$, $N(t)=320$. Thus, $A=320$. Also, from the exercise, the amount doubles every year, so $b=2$. Hence, we have:
$N(t)=320\cdot2^t$.
b) Thus, plugging in $t=8$, we get:
$N(8)=320\cdot2^{8}=81,920$ mice.
