Crown chakra puzzle

This page contains spoilers for the Iron Labyrinth One-shot

The Iron Labyrinth has six puzzles for players to solve. Of these, the Crown Chakra Puzzle is the only straightforward puzzle. The puzzle is a simple riddle that requires logical thought to complete

When the players enter the room, it is mostly empty. There is a large crown chakra symbol carved into the floor, which covers more than half the floor. In the center of the room their is a pedestal on which is carved the riddle:

One hundred elemental binders attend a tryout for the Caireal City Owlcats
100 of them can bind fire
90 of them can bind air
80 of them can bind water
75 of them can bind earth
At least how many of them can bind all four elements?

Also on the pedestal is a spherical glass case which contains an amethyst keystone. Without being able to touch the keystone, it is very difficult to know what benefit gives. It would require an Recall knowledge check (Difficulty 3) (Appraisal), or an Investigation check (Difficulty 4). If the players fail the check but get a score of two in either skill, they would know the list of possible bonuses that can be cut into an amethyst

The players need only to speak the correct answer and there will be a pleasant chime sound and the glass case will slide open. If the players give an incorrect answer, a harsh sounding bell sounds and nothing happens

For each incorrect answer given, reduce the points awarded when the puzzle is solved by 1 points

10 cannot bind air, 20 cannot bind water, and 25 cannot bind earth. Since we do not know how many of these people overlap, and the question asks us at least how many can bind all four elements, the worst case scenario is that these groups have no overlap. Therefore, as many as 45 cannot bind all four elements (10+20+25), which means that the remaining 55 would be able to bind all four elements

The amethyst inside the glass case has six facets and Sharp Mind 3. This grants a +3 bonus to a player's intelligence score if the stone is bound to the player's crown chakra. It can also be bound to the lotus chakra. An increase to a player's intelligence modifier grants:

• Six skill points. If you would like to simplify this bonus, allow a player to distribute 3d6 among their skills as desired
• A bonus to all Intelligence Checks
• A bonus to all Intelligence based Skills
• A bonus to all Intelligence based talents

Points
This is a straightforward puzzle and requires no special tricks