( 11 целых 3/10 - 8 целых 7/9) : 7 целых 17/30
=1/3
(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.