bjr
7/6 + 2/3 = 7/6 + 2x2/3x2 = 7/6 + 4/6 = 11/6
3/5 + 11/10 = 3x2/5x2 + 11/10 = 6/10 + 11/10 = 17/10
8/9 - 1/3 = 8/9 - 1x3/3x3 = 8/9 - 3/9 = 5/9
5 + 3/2 = 5/1 + 3/2 = 5x2/1x2 + 3/2 = 10/2 + 3/2 = 13/2
3 - 5/7 = 3/1 - 5/7 = 3x7/1x7 - 5/7 = 21/7 - 5/7 = 16/7