Which of the following are prime numbers?

Method: To test whether a number from the choices is prime, check divisibility by all prime numbers less than or equal to the square root of that number.

Check each candidate:

• 241: The square root of 241 is about 15.52, so test primes 2, 3, 5, 7, 11, and 13. 241 is not divisible by any of these primes, so 241 is prime.

• 303: Sum of digits is 3 + 0 + 3 = 6, so 303 is divisible by 3. Indeed, 303 = 3 × 101, so it is composite.

• 111: Sum of digits is 1 + 1 + 1 = 3, so 111 is divisible by 3. In fact, 111 = 3 × 37, so it is composite.

• 121: 121 = 11 × 11 (a perfect square), so it is composite.

Conclusion: 241 is the only prime number among the given choices.