(1/6+5/6) + (5/9+4/9) = 6/6+9/9 = 1+1=2
(2/17+5/17+10/17) + (3/8+5/8) = 17/17 + 8/8 = 1+1=2
(1/12+5/12) + (1/16+7/16) = 6/12 + 8/16 = 1/6 +1/8 = 8/48 + 6/48 = 14/48 = 7/24
(3/17+14/17) + (4/5+1/15) = 17/17 + (20/15+1/15) = 1 + 21/15 = 15/15+21/15 = 36/15 = 2 6/15