Question: what is the largest prime number that is a factor of 15?
Answer: 3 is a prime number because it has exactly two factors (1 and 3). 5 is a prime number because it has exactly two factors (1 and 5). 15 is not a prime number because it has four possible factors (1, 3, 5, and 15). Thus the prime factors of 15 are 3 and 5.