Solution
= Solution
Since $(1/2)^{3k}=(1/8)^k$, this is a <geometric series> of first term $1$ and common ratio $1/8$. Its sum is
$$
\boxed{\frac1{1-1/8}=\frac87.}
$$
= Solution
Since $(1/2)^{3k}=(1/8)^k$, this is a <geometric series> of first term $1$ and common ratio $1/8$. Its sum is
$$
\boxed{\frac1{1-1/8}=\frac87.}
$$