What is the probability that a randomly chosen integer is divisible by 2 or 3?

Approach: Use inclusion-exclusion principle on natural density.

1/2 + 1/3 - 1/6 = 2/3. The natural density of integers divisible by k is 1/k.

Follow-up: What about divisible by 2, 3, or 5?

Key concepts: natural density, inclusion-exclusion, divisibility.