So, by following this simple math, you can instantly generate the average hit points for a whole group of monsters without having to roll for each individual one. However, say you want to include some basic variation in your group of monsters, again, without having to roll a whole bunch of dice for each and every individual monster in a group. That's when I started thinking about how to make generically "stronger" or "weaker" individuals without having to roll their specific hit points. So I came up with a semi-simple compromise that lets me (fairly) quickly roll up some variable hit point individuals without just giving them all average hit points.
Kinda Quick Hit Points Determination (Roll 1d6):
|Roll||Type||1 HD||2 HD||3 HD||4 HD||5 HD||6+ HD|
|1||Skirmisher Mook||hp = 1||hp = 2||hp = 3||hp = 4||hp = 5||hp = #HD|
|2||Mook||hp = 2||hp = 4||hp = 6||hp = 8||hp = 10||hp = #HD + 1 HD|
|3||Upgraded Mook||hp = 3||hp = 6||hp = 9||hp = 12||hp = 15||hp = AVG hp - 1HD|
|4||Elite Mook||hp = 5||hp = 10||hp = 15||hp = 20||hp = 25||hp = AVG hp - 1HD|
|5||Lieutentant Mook||hp = 6||hp = 12||hp = 18||hp = 24||hp = 36||hp = Max hp - 1HD|
|6||King Mook||hp = 8||hp = Max hp||hp = Max hp||hp = Max hp||hp = Max hp||hp = Max hp|
Max hp = Hit Dice x 8.
AVG hp = 4.5 x the number of Hit Dice (rounded up).
#HD = the number of Hit Dice as hit points (i.e. a 7HD creature would have a value of 7).
When adding or subtracting 1HD from the results, this can be any number you choose (or choose to roll), for example, you could add or subtract 1 hp, average hp (5 in this case), or full hp (8) from the hp already determined.
For creatures (like say a creature with 6+1 HD or a creatures with 3-1 HD) just add or subtract the modifier after determining the hit points.