Let's analyze the given options to determine which statement is true:

• Option a: 15 is a prime number.

  • This is false. A prime number has only two divisors: 1 and itself. However, 15 has divisors 1, 3, 5, and 15, so it is not a prime number.

• Option b: –1 is a prime number.

  • This is false. Prime numbers are defined only for positive integers greater than 1, so negative numbers like –1 cannot be prime.

• Option c: –6 is a composite number.

  • This is false. Composite numbers are positive integers greater than 1 that have divisors other than 1 and itself. Since –6 is negative, it is not classified as composite.

• Option d: 27 is a composite number.

  • This is true. A composite number is a positive integer greater than 1 that has divisors other than 1 and itself. 27 has divisors 1, 3, 9, and 27, making it a composite number.

• Option e: 11 is not a prime number.

  • This is false. 11 is a prime number because it has no divisors other than 1 and 11.

The correct answer is d: 27 is a composite number.

Would you like more details or have any further questions? Here are some related questions to explore:

1. What is the difference between prime and composite numbers?
2. Can negative numbers ever be considered prime or composite?
3. How can you quickly determine whether a number is prime?
4. What are the divisors of composite numbers like 27?
5. Why is 11 considered a prime number?

Tip: A prime number is always a positive integer greater than 1, with exactly two divisors: 1 and itself.