[V.Rattanapon]

\[
\# 8
\]
น่าจะแก้เป็น \[
\frac{1}{{11}} - \frac{1}{{1100}} + \frac{1}{{111}} - \frac{1}{{111000}} + \frac{1}{{1111}} - \frac{1}{{11110000}} + ... = \frac{1}{{10}} = 0.1
\]