\(\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{4}\right)\cdot\left(1-\frac{1}{5}\right)=\frac{b}{100}\)
\(\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot\frac{4}{5}=\frac{b}{100}\)
\(\frac{1}{5}=\frac{b}{100}\)
\(\Rightarrow b=100\div5\times1=20\)
B=0
Vì 1-1/2=0/2=>0/2=0 như thế mà tính