Giải câu 98 bài: Ôn tập chương 1 sgk Toán 7 tập 1 Trang 49
Câu 98: trang 49 sgk toán lớp 7 tập 1
Tìm y biết:
a. $-\frac{3}{5}.y=\frac{21}{10}$;
b. $y\div \frac{3}{8}=-1\frac{31}{33}$;
c. $1\frac{2}{5}.y+\frac{3}{7}=-\frac{4}{5}$;
d. $-\frac{11}{12}.y+0,25=\frac{5}{6}$.
a. $\frac{-3}{5}.y=\frac{21}{10}$
$y=\frac{21}{10}\div \frac{-3}{5}$
$y=\frac{21}{10}.\frac{-5}{3}$
$y=\frac{-7}{2}$
b. $y\div \frac{3}{8}=-1\frac{31}{33}$
$y\div \frac{3}{8}=\frac{-64}{33}$
$y=\frac{-64}{33}.\frac{3}{8}$
$y=\frac{-8}{11}$
c. $1\frac{2}{5}.y+\frac{3}{7}=-\frac{4}{5}$
$\frac{7}{5}.y=-\frac{4}{5}-\frac{3}{7}$
$\frac{7}{5}.y=-\frac{28}{35}-\frac{15}{35}$
$\frac{7}{5}.y=\frac{-43}{35}$
$y=\frac{-43}{35}\div \frac{7}{5}$
$y=\frac{-43}{35}. \frac{5}{7}$
$y=\frac{-43}{49}$
d. $-\frac{11}{12}.y+0,25=\frac{5}{6}$
$-\frac{11}{12}.y+\frac{1}{4}=\frac{5}{6}$
$-\frac{11}{12}.y=\frac{5}{6}-\frac{1}{4}$
$-\frac{11}{12}.y=\frac{10}{12}-\frac{3}{12}$
$-\frac{11}{12}.y=\frac{7}{12}$
$y=\frac{7}{12}\div \frac{-11}{12}$
$y=\frac{7}{12}.\frac{-12}{11}$
$y=\frac{-7}{11}$
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