Answer For the number 11, the pairs would be 0 and 11, 1 and 10, 2 and 9, 3 and 8, 4 and 7, 5 and 6. There are 6 of these.
For even numbers there are n/2 + 1 ways, where n is the number. For odd numbers there are n/2 + 1 ways, where n is the number, and any halves are dropped. |