If n₁,…,nₖ are pairwise coprime, the system x ≡ a₁ (mod n₁), …, x ≡ aₖ (mod nₖ) has a unique solution modulo N = n₁n₂…nₖ.. The key formula is Unique solution mod N = n₁·n₂·…·nₖ. This concept is typically introduced in College. Understanding this concept builds a strong foundation for more advanced mathematics.