A) $\frac{12}{5}$ . 4 - 4 . $\frac{5}{7}$
= 4 . ($\frac{12}{5}$ - $\frac{5}{7}$)
= 4 . 1$\frac{24}{35}$
= 6$\frac{26}{35}$
B) $\frac{315}{316}$ . $\frac{313}{314}$ . $\frac{316}{315}$ . $\frac{317}{313}$
= $\frac{315.313.316.317}{316.314.315.313}$
= $\frac{317}{314}$
Chúc học tốt!!!