Ta có : \(A=\frac{40}{31.39}+\frac{35}{39.46}+\frac{30}{46.52}+\frac{25}{52.57}=5\left(\frac{8}{31.39}+\frac{7}{39.46}+\frac{6}{46.52}+\frac{5}{52.57}\right)\)
\(=5\left(\frac{1}{31}-\frac{1}{39}+\frac{1}{39}-\frac{1}{46}+\frac{1}{46}-\frac{1}{52}+\frac{1}{52}-\frac{1}{57}\right)=5\left(\frac{1}{31}-\frac{1}{57}\right)=5.\frac{26}{1767}=\frac{130}{1767}\)