\(B=\left(1-\frac{1}{3}\right)+\left(1-\frac{1}{3^2}\right)+...+\left(1-\frac{1}{3^{98}}\right)\)
\(B=\left(1+1+1+...+1\right)-\left(\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{98}}\right)\)
\(B=98-\left(\frac{1}{3}-\frac{1}{3^2}+...+\frac{1}{3^{98}}\right)<98\)
=>B<98<100
=>B<100 (đpcm)