(5/11 + 6/11) + (13/21 + 8/21)
= 1 + 1
= 2
\(\dfrac{5}{11}+\dfrac{13}{21}+\dfrac{6}{11}+\dfrac{8}{21}\\ =\left(\dfrac{5}{11}+\dfrac{6}{11}\right)+\left(\dfrac{13}{21}+\dfrac{8}{21}\right)\\ =\dfrac{11}{11}+\dfrac{21}{21}\\ =1+1\\ =2\)
= (5/11 + 6/11) + (13/21 + 8/21)
= 1 + 1
= 2
Vậy giá trị biểu thức là 2