31 13/16 + 13 17/28 = 509/16 + 381/28 =(509 × 7 + 381 × 4)/112 = (3563 + 1524)/112 = 5087/112 = 45 47/112
(43 7/9+45 3/8) - 62 3/8=26 7/9
1) 43 7/9 + 45 3/8 = 394/9 + 363/8 =(394 × 8 + 363 × 9)/72 = (3152 + 3267)/72 = 6419/72 = 89 11/72
2) 89 11/72 - 62 3/8 = 6419/72 - 499/8 =(6419 × 1 - 499 × 9)/72 = (6419 - 4491)/72 = 1928/72 = 241/9 = 26 7/9