tính giá trị biểu thức sau `298/719`:(`1/4`+`1/12`-`1/3`)-`2011/2012` `27.18+27.103-120.27/15.33+33.12` rút gọn B=(1-`1/2`).(1-`1/3`).(1-`1/4`)…….

a)=$\frac{298}{719}$ :($\frac{1}{4}$ +$\frac{1}{12}$- $\frac{1}{3}$ )-$\frac{2011}{2012}$ 

 =$\frac{298}{719}$ :0-$\frac{2011}{2012}$ 

=-$\frac{2011}{2012}$ 

b)$\frac{27.18+27.103-120.27}{15.33+33.12}$ 

=$\frac{27.(18+103-120}{33.(15+12}$

=$\frac{27.1}{33.27}$

=$\frac{1}{33}$

B=$\frac{1}{2}$ .$\frac{2}{3}$ .$\frac{3}{4}$ …$\frac{19}{20}$ 

B=$\frac{1.2.3..19}{2.3.4..20}$ 

B=$\frac{1}{20}$