[gpmedia]

Excellent point. The alternatives given should 15, 16-20, 21-25 etc.

Given this you should pick 20-25 (21-25) if you're 25.

[screwperman]

Most programmers have the habit of using asymmetric bounds i.e. lower bound included, upper bound excluded.

[Hexstream]

Yes.

http://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EW...