🎓 Deeper Dive — Adults

Addition is the simplest binary operation — but it has deep properties that underpin algebra.

Commutative: a + b = b + a. Associative: (a+b)+c = a+(b+c). Identity: a + 0 = a. These three properties define an abelian group on the integers.

Carrying in column addition is the everyday algorithm. Mental tricks: round and adjust (97+38 → 100+38−3 = 135).