Archivist Lyra · Mission briefing
Learn it by changing the world.
No worksheet detour. Identify the unknown, move the gems yourself, and make every number agree.
The gate chest has been raided
What do we need to discover?
Eighteen moon gems guarded the gate. A goblin carried seven away. Before calculating, name the part the story does not tell us.
Choose the missing part—not the final number yet.
Model the goblin raid
Move exactly seven gems.
Tap a gem to move it from the chest into the goblin’s satchel. Tap a moved gem to return it.
Moon chest · 18 remain
Goblin satchel · 0 of 7
Forge the proof
Tell the story in numbers.
Use your model to finish each line. The proof is complete only when the starting amount, change, and remainder all agree.
Moon gems started
Moon gems taken
Moon gems stayed
Build all three parts from the model you just made.
Parent check: the learner should name 18 starting gems, 7 taken gems, and 11 remaining gems.
Rune proof sealed
You are ready for the Dragon Test.
The lesson taught the model. The playable room now tests whether you can use it inside the adventure—without the answer being handed to you.
“I started with 18 moon gems, took away 7, and counted 11 remaining. That matches 18 - 7 = 11.”