1)(1 3/13+2 2/13)+3 7/13 = 3 5/13+3 7/13 = 6 12/13
2) 5 7/18 + (4 11/18 + 2 10/18) = 5 7/18 + 6 21/18 = 11 28/18 = 12 10/18 = 12 5/9
3) 5 6/17 +(6 16/17 + 13 8/17) = 5 6/17 + 19 24/17 = 24 30/17 = 25 13/17
4) 1116/23 + (4 14/23 +7 13/23) = 11 16/23 + 11 27/23 = 22 43/23 = 23 20/23