8 7/30 - 2 9/20 = 247/30 - 49/20 = (247 × 2 - 49 × 3)/60 = 494/60 - 147/60 = 347/60 = 5 47/607 10/51 - 4 21/34 = 367/51 - 157/34 = (367 × 2 - 157 × 3)/102 = 734/102 - 471/102 = 263/102 = 2 59/102
5 1/4 - 1 3/8 = 21/4 - 11/8 = (21 × 2 - 11 × 1)/8 = 42/8 - 11/8 = 31/8 = 3 7/8