b,7/8+5/6x=25% c,C=7/3.4+9/4.5+11/5.6-13/6.7+15/7.8-17/8.9+19/9.10

Đáp án:

 $a) x=-\dfrac{3}{4}$

$b) \dfrac{4}{3}$

Giải thích các bước giải:

$a) \dfrac{7}{8}+\dfrac{5}{6}x=25\%\\\Leftrightarrow \dfrac{7}{8}+\dfrac{5}{6}x=\dfrac{25}{100}\\\Leftrightarrow 525+500x=150\\\Leftrightarrow 500x=150-525\\\Leftrightarrow 500x=-375\\\Leftrightarrow x=-\dfrac{3}{4}\\b) \dfrac{7}{3.4}+\dfrac{9}{4.5}+\dfrac{11}{5.6}-\dfrac{13}{6.7}+\dfrac{15}{7.8}-\dfrac{17}{8.9}+\dfrac{19}{9.10}\\=\dfrac{7}{12}+\dfrac{9}{20}+\dfrac{11}{30}-\dfrac{13}{42}+\dfrac{15}{56}-\dfrac{17}{72}+\dfrac{19}{90}\\=\dfrac{1470+1134+924-780+675-595+532}{2520}\\=\dfrac{3360}{2520}=\dfrac{4}{3}$