Ответ:

  1. \(0{,}0000321=3{,}21\cdot10^{-5}\).
  2. \(0{,}000074=7{,}4\cdot10^{-5}\).
  3. \(31\frac25=31{,}4=3{,}14\cdot10^1\).
  4. \(1401\frac3{25}=1401{,}12=1{,}40112\cdot10^3\).