Question

Tính.

a) \(\dfrac{1}{7}+\dfrac{1}{9}\)                  \(\dfrac{3}{11}+\dfrac{7}{12}\)                \(\dfrac{13}{5}+\dfrac{7}{6}\)

b) \(\dfrac{1}{4}-\dfrac{1}{9}\)                   \(\dfrac{2}{5}-\dfrac{1}{4}\)                    \(\dfrac{11}{7}-\dfrac{5}{8}\)

Answer 1

a: 

\(\dfrac{1}{7}+\dfrac{1}{9}=\dfrac{9}{63}+\dfrac{7}{63}=\dfrac{9+7}{63}=\dfrac{16}{63}\)

\(\dfrac{3}{11}+\dfrac{7}{12}=\dfrac{36}{132}+\dfrac{77}{132}=\dfrac{113}{132}\)

\(\dfrac{13}{5}+\dfrac{7}{6}=\dfrac{78}{30}+\dfrac{35}{30}=\dfrac{78+35}{30}=\dfrac{113}{30}\)

b: 

\(\dfrac{1}{4}-\dfrac{1}{9}=\dfrac{9}{36}-\dfrac{4}{36}=\dfrac{9-4}{36}=\dfrac{5}{36}\)

\(\dfrac{2}{5}-\dfrac{1}{4}=\dfrac{8}{20}-\dfrac{5}{20}=\dfrac{8-5}{20}=\dfrac{3}{20}\)

\(\dfrac{11}{7}-\dfrac{5}{8}=\dfrac{11\times8-5\times7}{56}=\dfrac{88-35}{56}=\dfrac{51}{56}\)