a) \(\frac{21}{11}\cdot\frac{22}{17}\cdot\frac{68}{63}\)
\(=\frac{21\cdot22\cdot68}{11\cdot17\cdot63}\)
\(=\frac{3\cdot7\cdot2\cdot11\cdot4\cdot17}{11\cdot17\cdot7\cdot3\cdot3}\)
\(=\frac{2\cdot4}{3}\)
\(=\frac{8}{3}\)
b) \(\frac{5}{14}\cdot\frac{7}{13}\cdot\frac{26}{25}\)
\(=\frac{5\cdot7\cdot26}{14\cdot13\cdot25}\)
\(=\frac{5\cdot7\cdot2\cdot13}{2\cdot7\cdot13\cdot5\cdot5}\)
\(=\frac{1}{5}\)
=))