2. 11 + 13 + 15 + 17 + 19 + 31 + 33 + 35 + 37 + 39 + 51 + 53 + 55 + 57 + 59 + 71 + 73 + 75 + 77 + 79 + 91 + 93 + 95 + 97 + 99 = 1375
4. 14, 16, 18, 23, 25, 27, 32, 34, 36, 41, 43, 45, 50, 52, 54, 59, 61, 63, 68, 70, 72, 77, 81, 86, 90, 95.
5. 81 - 67 = 14; 75 - 61 = 14; 67 - 53 = 14; 89 - 15 = 74; 87 - 13 = 74; 85 - 11 = 74.