Đáp án:
`A=0`
Giải thích các bước giải:
$A=\dfrac{ 0,25+\dfrac{1}{5}-\dfrac{1}{6} } { 0,5 + \dfrac{2}{5}- \dfrac{1}{3}} -\dfrac{0,2-\dfrac{1}{6}+\dfrac{1}{7}} {0,4-\dfrac{1}{3}+\dfrac{2}{7}}$
$=\dfrac{\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{6}}{\dfrac{1}{2}+\dfrac{2}{5}-\dfrac{1}{3}} - \dfrac{\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{7}}{\dfrac{2}{5}-\dfrac{1}{3}+\dfrac{2}{7}}$
$=\dfrac{\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{6}}{2.(\dfrac{1}{4}+\dfrac{1}{5}-\dfrac{1}{6})} - \dfrac{\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{7}}{2.(\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{7})}$
`=1/2 - 1/2 = 0`
Vậy `A=0`
