Câu 11: B
Câu 13: \(\dfrac{2}{6}+\dfrac{1}{4}+\dfrac{5}{6}=\dfrac{17}{12}\)
\(\dfrac{1}{5}+\dfrac{2}{3}=\dfrac{3}{15}+\dfrac{10}{15}=\dfrac{13}{15}\)
\(\dfrac{1}{4}+\dfrac{7}{4}+\dfrac{4}{7}=2+\dfrac{4}{7}=\dfrac{18}{7}\)
Câu 14:
\(\dfrac{13}{11}+\dfrac{7}{11}+\dfrac{4}{11}=\dfrac{13+7+4}{11}=\dfrac{24}{11}\)