\(a.8.5+\left(-3\right).9\)
\(=40+-27\)
\(=-13\)
\(a,8\times5+(-3)\times9=40+(-27)=13\)
\(b,\frac{2}{5}+\frac{1}{5}\times\left[\frac{-3}{4}\right]\)
\(=\frac{2}{5}+\frac{-3}{20}\)
\(=\frac{8}{20}+\frac{-3}{20}=\frac{5}{20}=\frac{1}{4}\)
\(c,2:\left[\frac{1}{2}-\frac{2}{3}\right]=2:\left[\frac{3}{6}-\frac{4}{6}\right]=2:\frac{-1}{6}=2\times\frac{6}{-1}=-12\)
\(b.\frac{2}{5}+\frac{1}{5}\times\frac{-3}{4}\)
\(=\frac{2}{5}+\frac{-3}{20}\)
\(=\frac{8}{20}+\frac{-3}{20}\)
\(=\frac{5}{20}\)
\(=\frac{1}{4}\)
\(c.2:\left(\frac{1}{2}-\frac{2}{3}\right)\)
\(=2:\left(\frac{3}{6}-\frac{4}{6}\right)\)
\(=2:\frac{-1}{6}\)
\(=\frac{12}{-1}\)
\(=\frac{-12}{1}=-12\)