Answer
See below
Work Step by Step
From exercise 4, we found $a_n=2^{n-1}$
The number of people in her family tree can be found by finding the sum of the first 8 terms with $a_1=1, r=2$:
$$\sum^8_{i=1}2^{i-1}\\=a_1\frac{1-r^n}{1-r}\\=1\times\frac{1-2^8}{1-2}=255$$
Hence, there are 255 people in the family tree.
