a)\(\frac{3}{7}\cdot19\frac{1}{3}-\frac{3}{7}\cdot33\frac{1}{3}\)
\(=\frac{3}{7}\cdot\left(19\frac{1}{3}-33\frac{1}{3}\right)\)
\(=\frac{3}{7}\cdot\left[\left(19-33\right)-\left(\frac{1}{3}-\frac{1}{3}\right)\right]\)
\(=\frac{3}{7}\cdot\left[\left(-14\right)-0\right]\)
\(=\frac{3}{7}\cdot\left(-14\right)=-6\)
b)\(9\cdot\left(-\frac{1}{3}\right)^3+\frac{1}{3}\)
\(=9\cdot\left(-\frac{1}{3}\right)^3-\left(-\frac{1}{3}\right)\)
\(=\left(-\frac{1}{3}\right)\cdot\left[9\cdot\left(-\frac{1}{3}\right)^2-1\right]\)
\(=\left(-\frac{1}{3}\right)\cdot\left[9\cdot\frac{1}{9}-1\right]\)
\(=\left(-\frac{1}{3}\right)\cdot\left[1-1\right]\)
\(=\left(-\frac{1}{3}\right)\cdot0=0\)
c)\(15\frac{1}{4}:\left(-\frac{5}{7}\right)-25\frac{1}{4}:\left(-\frac{5}{7}\right)\)
\(=\left(15\frac{1}{4}-25\frac{1}{4}\right):\left(-\frac{5}{7}\right)\)
\(=\left[\left(15-25\right)-\left(\frac{1}{4}-\frac{1}{4}\right)\right]\cdot\left(-\frac{7}{5}\right)\)
\(=\left[\left(-10\right)-0\right]\cdot\left(-\frac{7}{5}\right)\)
\(=\left(-10\right)\cdot\left(-\frac{7}{5}\right)=14\)
