Ответ:

  1. а) \(758\cdot89=758\cdot(90-1)=68\,220-758=67\,462\).
  2. б) \(400\cdot502=400\cdot(500+2)=200\,000+800=200\,800\).
  3. в) \(6100\cdot97\,000=61\cdot97\cdot100\,000=5\,917\cdot100\,000=591\,700\,000\).
  4. г) \(8\cdot51\cdot75=(8\cdot75)\cdot51=600\cdot51=30\,600\).