Ta có :
A = $\frac{13}{50} \times (-15.5) - \frac{13}{50} \times 84\frac{1}{2}$
= $\frac{13}{50} \times$ (-15.5 - 84.5) = $\frac{13}{50} \times$ (-100) = -26
$B = \frac{(-0.7)^{2} \times (-0.5)^{3}}{(\frac{-7}{3})^{3} \times (\frac{3}{2})^{4} \times (-1)^{5}}$
$= \frac{0.49 \times (-125)}{\frac{-343}{27} \times \frac{81}{16} \times (-1)}$
= $\frac{-61.25}{\frac{1029}{16}} = -61.25 / \frac{1029}{16} = \frac{-245}{4} \times \frac{16}{1029} = \frac{-20}{21}.$
Như vậy, bạn An đã tính đúng.