3 1/3 - 2,5 = 3 1/3 - 2 1/2 = (3*3+1)/3 - (2*2+1)/2 = 10/3 - 5/2 = (10*2)/(3*2) - (5*3)/(2*3) = 20/6 - 15/6 = (20-15)/6= 5/6
26 1/11 - 5,7 = 26 1/11 - 5 7/10 = (26*11+1)/11 - (5*10+7)/10 = 287/11 - 57/10 = (287*10)/(11*10) - (57*11)/(10*11) = 2870/110 - 627/110 = (2870-627)/110 = 2243/110 = 20 43/110
18 5/3 - 9,5 = 18 5/3 - 9 1/2 = (18*3+5)/3 - (9*2+1)/2 = 59/3 - 19/2 = (59*2)/(3*2) - (19*3)/(2*3) = 118/6 - 57/6 = (118-57)/6= 61/6 = 10 1/6