Mathematics discovery
Algebra Lab: Choose what belongs in the box so both trays hold five counters.
Represent an unknown quantity with a concrete box and preserve equality through matching moves.
The box symbol has a fixed value in every problem forever.
Open the box after the prediction and count both sides with the learner.
CCSS.MATH.1.OA.D.8 / CCSS.MATH.2.OA.A.1
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