( 11 целых 3/10 - 8 целых 7/9) : 7 целых 17/30

(11 3/10 - 8 7/9)/7 17/30 = (  9(113/10) - 10(79/9)  ) / 227/30 = (1017/90-790/90)*30/227 = 227/90 * 30/227 = 1/3.