How to solve door puzzles in Hogwarts Castle.
Arithmancy Study Guide Page
It's a page with numbers assigned to each magical beast that will help you solve the puzzle.
1. Open map of the Hogwarts castle and choose The Library Annex and then Divination Classroom.
2. Don't go up or down, look back and enter a wooden room.
3. Go forward and then to your first right to find a door puzzle with a box in front of it that contains the Arithmancy Study Guide Page.

Door Puzzle
1. After finding a door puzzle, get close to it and reveal it's puzzle with the Reveal button.
2. Each door has two beasts you need to find the number of.
3. To find the beast number you need to do a little math of the beast number and a already visible number to find the question number so all of them add up to the center number.
4. For example in the first door where you find the guide page the three head dragon is 3, the visible number is 2 and the center number is 9, which means if you do a math like 3+2+?=9 you get the number 4, which is the number for the beast you need to find in the question block.

5. After finding the number for each beast check the page again and reveal that beast in the question blocks (? and ??).
Answer of Door Puzzles
Library Annex 1

- The Library Annex > Divination Classroom > Don't go up or down, look back and enter a wooden room and then go right.
Library Annex 2

- Inside Library Annex 1.
Library Annex 3

- Inside Library Annex 1.
The Bell Tower Wing

- The Bell Tower Wing > Bell Tower Courtyard > Open the door next to you and go down.
Central Hall

- The Library Annex > Central Hall > Go down the stairs behind you and then down the stairs in your left.
Ravenclaw Tower

- The Grand Staircase > Ravenclaw Tower.
Grand Staircase Tower

- The Grand Staircase > Grand Staircase Tower > Go down the stairs.
The Great Hall

- The Great Hall > Great Hall > Go left.
Bell Tower Courtyard

- The Bell Tower Wing > Bell Tower Courtyard > go way up the stairs in your left until you can no longer up go, there will be a door with a door puzzle inside it.
Charms Classroom

- The Astronomy Wing > Charms Classroom > Look behind yourself to find it.
Grand Staircase

- The Grand Staircase > Grand Staircase > Use Revelio spell to see it up the stairs in your left.
Hospital Wing

- The South Wing > Hospital Wing > Keep going down the stairs until you see the puzzle door in front of you.