1) 8,5 - 1/3 = 85/10 - 1/3 = 225/30 - 10/30 = 215/30 = 7 5/30 = 7 1/6
2) 4 1/9 + 1,8 = 4 1/9 + 1 8/10 = (4 + 1) + (1/9 + 8/10) = 5 + (10/90 + 72/90) = 5 + 82/90 = 5 41/45
3) 1/9 * 0,12 = 1/9 * 12/100 = 12/900 = 1/75
4) 6/7 / 0,6 = 6/7 / 6/10 = 10/7 = 1 3/7