Đáp án + Giải thích các bước giải:

`1.`

`a)` `A =` $\frac{\dfrac{3}{4} - \dfrac{3}{11} + \dfrac{3}{13}}{\dfrac{5}{4} - \dfrac{5}{11} + \dfrac{5}{13}}$ `+` $\frac{\dfrac{1}{2} - \dfrac{1}{3} + \dfrac{1}{4}}{\dfrac{5}{2} - \dfrac{5}{3} + \dfrac{5}{4}}$

    `A =` $\frac{3 (\dfrac{1}{4} -\dfrac{1}{11} + \dfrac{1}{13})}{5(\dfrac{1}{4}-\dfrac{1}{11}+\dfrac{1}{13})}$ `+` $\frac{\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{4}}{5(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{4})}$

    `A =` `3/5` `+` `1/5`

        `= 4/5`

Vậy `A = 4/5`

`#yayfisi``ng`