Đáp án: $A=\dfrac{13}{48}$
Giải thích các bước giải:
Ta có :
$A=\dfrac{1}{16}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}$
$\to A=\dfrac{1}{16}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}$
$\to A=\dfrac{1}{16}+\dfrac{4-3}{3.4}+\dfrac{5-4}{4.5}+\dfrac{6-5}{5.6}+\dfrac{7-6}{6.7}+\dfrac{8-7}{7.8}$
$\to A=\dfrac{1}{16}+\dfrac13-\dfrac14+\dfrac14-\dfrac15+\dfrac15-\dfrac16+\dfrac16-\dfrac17+\dfrac17-\dfrac18$
$\to A=\dfrac1{16}+\dfrac13-\dfrac18$
$\to A=\dfrac{13}{48}$
