\(A=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{100}}\)
=>\(2A=2+1+\frac{1}{2}+...+\frac{1}{2^{99}}\)
=>\(2A-A=2+1+\frac{1}{2}+...+\frac{1}{2^{99}}-1-\frac{1}{2}-\frac{1}{2^2}-\frac{1}{2^3}-...-\frac{1}{2^{100}}\)
=>\(A=2-\frac{1}{2^{100}}=\frac{2^{101}}{2^{100}}-\frac{1}{2^{100}}\)
=>\(A=\frac{2^{101}-1}{2^{100}}\)