\(a)\frac{1}{5}\times\frac{1}{2}:\frac{1}{3}=\frac{1}{5}\times\frac{1}{2}\times\frac{3}{1}=\frac{1\times1\times3}{5\times2\times1}=\frac{1\times3}{5\times2}=\frac{3}{10}\)
\(b)\frac{2}{9}:\frac{2}{3}\times\frac{1}{2}=\frac{2}{9}\times\frac{3}{2}\times\frac{1}{2}=\frac{2\times3\times1}{9\times2\times2}=\frac{1\times1\times1}{3\times1\times2}=\frac{1}{6}\)
\(c)\frac{1}{2}\times\frac{1}{3}+\frac{1}{4}=\frac{1}{6}+\frac{1}{4}=\frac{2}{12}+\frac{3}{12}=\frac{2+3}{12}=\frac{5}{12}\)
d, Tương tự như câu c
P/S : Bất phương trình????
\(\frac{1}{5}\times\frac{1}{2}:\frac{1}{3}\)
\(=\frac{1}{10}\times\frac{3}{1}\)
\(=\frac{3}{10}\)
\(\frac{2}{9}:\frac{2}{3}\times\frac{1}{2}\)
\(=\frac{2}{9}\times\frac{3}{2}\times\frac{1}{2}\)
\(=\frac{1}{3}\times\frac{1}{1}\times\frac{1}{2}\)
\(=\frac{1}{3}\times\frac{1}{2}\)
\(=\frac{1}{6}\)
\(\frac{1}{2}\times\frac{1}{3}+\frac{1}{4}\)
\(=\frac{1}{6}+\frac{1}{4}\)
\(=\frac{4}{24}+\frac{6}{24}\)
\(=\frac{10}{24}\)\(=\frac{5}{12}\)
\(\frac{2}{7}:\frac{2}{3}-\frac{1}{7}\)
\(=\frac{2}{7}\times\frac{3}{2}-\frac{1}{7}\)
\(=\frac{3}{7}-\frac{1}{7}\)
\(=\frac{2}{7}\)