Answer
$0.00000004$
Work Step by Step
The $n^{th}$ term of a geometric sequence is given by the formula:
$ a_n=a_1r^{n-1}$
where $r$=common ratio and $a_1$= the first term
The common ratio of a geometric sequence is equal to the quotient (ratio) of any term and the term before it:
$ \ r = \dfrac{a_n}{a_{n-1}}$ or, $r=\dfrac{a_2}{a_1}$
Here $a_1=0.4$ and and $a_2=0.04$, so $r=\dfrac{0.04}{0.4}=0.1$
So, $a_n=(0.4)(0.1)^{n-1}$
Therefore, $a_{8}=(0.4)(0.1)^{8-1} \approx 0.00000004$
