Ta có:
`A=`$\frac{4}{7.31}$ `+` $\frac{6}{7.41}$ `+` $\frac{9}{10.41}$ `+`$\frac{7}{10.57}$
`A=`$\frac{20}{31.35}$ `+` $\frac{30}{35.41}$ `+` $\frac{45}{41.50}$ `+` $\frac{35}{50.57}$
`A=5(`$\frac{4}{31.35}$ `+` $\frac{6}{35.41}$ `+` $\frac{9}{41.50}$ `+` $\frac{7}{50.57}$`)`
`A=5(`$\frac{1}{31}$`-` $\frac{1}{35}$ `+` $\frac{1}{35}$ `-` $\frac{1}{41}$ `+` $\frac{1}{41}$ `-` $\frac{1}{50}$ `+`$\frac{1}{50}$ `-`$\frac{1}{57}$`)`
`A=5(` $\frac{1}{31}$ `-` $\frac{1}{57}$`)` `(1)`
Lại có:
`B=`$\frac{7}{19.31}$ `+` $\frac{5}{19.43}$ `+` $\frac{3}{23.43}$ `+` $\frac{11}{23.57}$
`B=`$\frac{14}{38.31}$ `+` $\frac{10}{38.43}$ `+` $\frac{6}{46.43}$ `+` $\frac{22}{46.57}$
`B=2(`$\frac{7}{31.38}$ `+`$\frac{5}{38.43}$ `+` $\frac{3}{43.46}$ `+` $\frac{11}{46.57}$`)`
`B=2(`$\frac{1}{31}$ `-` $\frac{1}{38}$ `+` $\frac{1}{38}$ `-` $\frac{1}{43}$ `+` $\frac{1}{43}$ `-` $\frac{1}{46}$ `+` $\frac{1}{46}$ `-` $\frac{1}{57}$ `)`
`B=2(`$\frac{1}{31}$ `-` $\frac{1}{57}$`)` `(2)`
Từ `(1)` và `(2)` ta suy ra `A/B=` $\frac{5(\frac{1}{31}-\frac{1}{57})}{2(\frac{1}{31}-\frac{1}{57})}$ `=5/2`
Vậy: `A/B=5/2`
$\color{Pink}{\text{#Keongotzzz}}$
