a)

• $\frac{3}{8} = \frac{3\times 27}{8\times 27} = \frac{81}{216}$;
• $\frac{7}{27} = \frac{7\times 8}{27\times 8} = \frac{56}{216}$;

b)

• $\frac{-5}{9} = \frac{-5\times 25}{9\times 25} = \frac{-125}{225}$;
• $\frac{4}{25} = \frac{4\times 9}{25\times 9} = \frac{36}{225}$;

c)

• $\frac{1}{11}$;
• $-6 = \frac{-6}{1} = \frac{-6\times 11}{1\times 11} = \frac{-66}{11}$;

d

• $\frac{13}{120}$;
• $\frac{7}{40} = \frac{7\times 3}{40\times 3} = \frac{21}{120}$;

e) Rút gọn phân số: $\frac{14}{146} = \frac{7}{73}$

• $\frac{7}{73} = \frac{7\times 13}{73\times 13} = \frac{91}{949}$;
• $\frac{6}{13} = \frac{6\times 73}{13\times 73} = \frac{438}{949}$;

g)

• $\frac{-7}{30} = \frac{-7\times 4}{30\times 4} = \frac{-28}{120}$;
• $\frac{13}{60} = \frac{13\times 2}{60\times 2} = \frac{26}{120}$;
• $\frac{-9}{40} = \frac{-9\times 3}{40\times 3} = \frac{-27}{120}$;

h) Rút gọn: $\frac{64}{90} = \frac{32}{45};

• $\frac{-17}{60} = \frac{-17\times 3}{60\times 3} = \frac{51}{180}$;
• $\frac{-5}{18} = \frac{-5\times 10}{18\times 10} = \frac{-50}{180}$;
• $\frac{64}{90} = \frac{32}{45} = \frac{32\times 4}{45\times 4} = \frac{128}{180}$;