Ответ:

  1. \(\frac78p\cdot\frac49k=\frac7{18}pk.\)
  2. \(1\frac57x\cdot\frac5{12}y=\frac{12}{7}x\cdot\frac5{12}y=\frac57xy.\)
  3. \(2\frac58x\cdot2y\cdot2\frac27z=\frac{21}{8}x\cdot2y\cdot\frac{16}{7}z=12xyz.\)