Question: prove 10^n+1+10n+1 is divisible by 3?
Answer: (10 points) Prove that 10n+1 + 10n + 1 is divisible by 3 for n ∈ N. Solution: If n = 1, then 10n+1 + 10n + 1 = 111 is divisible by 3. ... Therefore, the statement is true for all natural numbers by the Principle of Mathematical Induction.