Ответ:

  • а) 4/5 + 3/7 = 28/35 + 15/35 = 43/35.
  • б) 5/12 + 9/20 = 25/60 + 27/60 = 52/60 = 13/15.
  • в) 5/18 + 4/45 = 25/90 + 8/90 = 33/90 = 11/30.
  • г) 12/17 + 27/34 = 24/34 + 27/34 = 51/34 = 3/2.