1)11/12+2/15 2)2 целых 5/21+ 1 целых 9/14 3) 5-(9/10 - 4/15)

11,12+2,15=13,27
2 5/12 +1 9/14= 3 (5×14)+(9×12)/168= 3 (70+108)/168=3 178/168=4 10/168=4 5/84
5 9/10-4/15= 5 ((9×2)-(4×3)/30=5 (18-12)30=
=5 4/30=5 2/15