A = 1/5 + 1/10 + 1/20 + 1/40 + 1/80 +1/160 + 1/320 + 1/640 + 1/1280
A x 2 = 2/5 + 1/5 + 1/10 + 1/20 + 1/40 + 1/80 +1/160 + 1/320 + 1/640
A x 2 - A = A = 2/5 - 1/1280 = 511/1280
\(\frac{1}{5}\)+\(\frac{1}{10}\)+\(\frac{1}{20}\)+\(\frac{1}{40}\)+\(\frac{1}{80}\)+\(\frac{1}{160}\)+\(\frac{1}{320}\)+\(\frac{1}{640}\)+\(\frac{1}{1280}\)
=\(\frac{511}{1280}\)