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Câu b:
\(\frac{21}{8}:\frac{5}{6}+\frac{1}{2}:\frac{5}{6}\)
= \(\frac{63}{20}+\frac{3}{5}\)
= \(\frac{15}{4}\)
\(\left(\frac{21}{8}+\frac{1}{2}\right):\frac{5}{6}\)
\(\frac{25}{8}:\frac{5}{6}\)
\(\frac{25}{8}.\frac{6}{5}\)
\(\frac{30}{8}\)
\(a,\left(16.23+16.77\right)-\left(5.30-5.20\right)\)
\(=16.\left(23+77\right)-5.\left(30-20\right)\)
\(=16.100-5.10\)
\(=1600-50\)
\(=1550\)
\(b,8\frac{1}{2}\div\frac{17}{5}+\frac{6}{8}\div3\frac{2}{3}\)
\(=\frac{17}{2}.\frac{5}{17}+\frac{3}{4}\div\frac{11}{3}\)
\(=\frac{17}{2}.\frac{5}{17}+\frac{3}{4}.\frac{3}{11}\)
\(=\frac{5}{2}+\frac{9}{44}\)
\(=\frac{110}{44}+\frac{9}{44}\)
\(=\frac{119}{44}\)
\(a,=16.100-5.10=1600-50=1550\)
\(b,8\frac{1}{2}:\frac{17}{5}+\frac{6}{8}:3\frac{2}{3}=\frac{17}{2}.\frac{5}{17}+\frac{6}{8}:\frac{11}{3}=\frac{5}{2}+\frac{18}{88}=\frac{220}{88}+\frac{18}{88}=\frac{238}{88}=2\frac{31}{44}\)
Ta có:
\(A=\left(x-\frac{1}{2}\right).\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)=\frac{1}{3}\)
\(\Leftrightarrow A=\left(x-\frac{1}{2}\right).\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)=\frac{1}{3}\)
\(\Leftrightarrow A=\left(x-\frac{1}{2}\right).\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right)=\frac{1}{3}\)
\(\Leftrightarrow A=\left(x-\frac{1}{2}\right).\left(\frac{1}{1}-\frac{1}{10}\right)=\frac{1}{3}\)
\(\Leftrightarrow A=\left(x-\frac{1}{2}\right).\frac{9}{10}=\frac{1}{3}\Leftrightarrow x-\frac{1}{2}=\frac{1}{3}.\frac{10}{9}\Leftrightarrow x=\frac{47}{54}\)
\(B=\frac{1}{1.6}+\frac{1}{6.11}+\frac{1}{11.16}+...+\frac{1}{96.101}=\frac{1}{10.x}\)
\(\Leftrightarrow B=\frac{1}{5}.\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{5}{96.101}\right)=\frac{1}{10}-\frac{1}{x}\)
\(\Leftrightarrow B=\frac{1}{5}.\left(\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{96}-\frac{1}{101}\right)=\frac{1}{10}-\frac{1}{x}\)
\(\Leftrightarrow B=\frac{1}{5}.\left(\frac{1}{1}-\frac{1}{101}\right)=\frac{1}{10}-\frac{1}{x}\Leftrightarrow B=\frac{1}{5}.\frac{100}{101}=\frac{1}{10}-\frac{1}{x}\)
\(\Leftrightarrow B=\frac{1}{x}=\frac{1}{10}-\frac{20}{101}=-\frac{99}{1010}\Leftrightarrow x=-\frac{1010}{99}\)
c) Sai đề nhé bạn vì không có kết quả nên không tìm được x.
d) \(\left(x-5\right).\left(10-9\frac{40}{41}\right):\left(1-\frac{81}{82}\right):\left(1-\frac{204}{205}\right)=2050\)
\(\Rightarrow\left(x-5\right).\frac{1}{41}.82.205=2050\)
\(\Rightarrow\left(x-5\right).2.205=2050\Leftrightarrow x-5=2050:410=5\Leftrightarrow x=10\)
a) \(10-\frac{9}{16}=\frac{160}{16}-\frac{9}{16}=\frac{151}{16}\)
b) \(\frac{2}{3}-\left(\frac{1}{6}+\frac{1}{8}\right)=\frac{2}{3}-\frac{1}{6}-\frac{1}{8}=\frac{16}{24}-\frac{4}{24}-\frac{3}{24}=\frac{9}{24}=\frac{3}{8}\)
a)10-\(\frac{9}{16}\)
=\(\frac{160}{16}-\frac{9}{16}\)
\(=\frac{151}{16}\)
b)\(\frac{2}{3}-\left(\frac{1}{6}+\frac{1}{8}\right)\)
=\(\frac{2}{3}-\left(\frac{4+3}{24}\right)\)
=\(\frac{2}{3}-\frac{7}{24}=\frac{16-7}{24}\)
=\(\frac{3}{8}\)