How can you add five matches to six matches to make nine?

Answer 1

Answer: Mathematically, it is impossible to add five matches to six matches to result in nine matches.

Logically, however, you can add five matches to six matches to make nine if one match is on fire, then you set that match on another match, and eventually both of those matches that were on fire burn themselves into ashes, leaving you with only nine unlit matches left.

Answer: You lay out the 11 matches so they spell the word NINE.