2.193

a) 1/5 + 1/7 = (7+5)/35 = 12/35. b) 1/2 + 2/3 = (3+4)/6 = 7/6. c) 3/5 + 4/7 = (21+20)/35 = 41/35. d) 8/15 + 3/10 = (16+9)/30 = 25/30 = 5/6.