\(x=\dfrac{12\times7}{4}=21\)

4x 3/7x 3=12/21=4/7

\(\dfrac{1}{2}=\dfrac{6}{12};\dfrac{2}{3}=\dfrac{8}{12};\dfrac{7}{12}=\dfrac{7}{12}\)

Chắc là quy đồng nhỉ :)

\(\dfrac{1\times6}{2\times6}=\dfrac{6}{12};\dfrac{2\times4}{3\times4}=\dfrac{8}{12};\dfrac{7}{12}\)

6/12

8/12

7/12 

18

18

18

124

124

126

\(=\dfrac{10}{15}+\dfrac{6}{15}=\dfrac{16}{15}\)

10/15+6/15

16/15

\(\dfrac{2}{3}+\dfrac{2}{5}=\dfrac{10}{15}+\dfrac{6}{15}=\dfrac{16}{15}\)

7/8-1/2=3/8

7/8 - 1/2

= 7/8- 4/8

= 3/8

\(=\dfrac{3}{8}\)

\(\dfrac{12}{6}+\dfrac{15}{7}=\dfrac{84}{42}+\dfrac{90}{42}=\dfrac{174}{42}=\dfrac{29}{7}\)

\(\dfrac{12}{13}-\dfrac{8}{9}=\dfrac{108}{117}-\dfrac{104}{117}=\dfrac{4}{117}\)

\(\dfrac{43}{54}+\dfrac{76}{8}=\dfrac{344}{432}+\dfrac{4104}{432}=\dfrac{4448}{432}=\dfrac{278}{27}\)

\(\dfrac{12}{6}+\dfrac{15}{7}=2+\dfrac{15}{7}=\dfrac{14}{7}+\dfrac{15}{7}=\dfrac{29}{7}\\ \dfrac{12}{13}-\dfrac{8}{9}=\dfrac{108}{117}-\dfrac{104}{117}=\dfrac{4}{117}\\ \dfrac{43}{54}+\dfrac{76}{8}=\dfrac{43}{54}+\dfrac{19}{2}=\dfrac{43}{54}+\dfrac{513}{54}=\dfrac{556}{54}=\dfrac{278}{27}\)

A

D

d

7 hours 15 minutes