Final answer:
To find which number is composite, we can look for divisibility by primes. Numbers ending in 5 are divisible by 5, making them composite. Thus, out of the choices given, the number 555 is the composite number.
Step-by-step explanation:
The student's question asks which one of the given numbers is composite. A composite number is a positive integer that has at least one divisor other than 1 and itself. To determine which number is composite, we look for a number that can be divided evenly by numbers other than 1 and itself.
The process involves checking each number by attempting to divide it by the smallest prime numbers such as 2, 3, 5, 7, etc., until we find a divisor or determine that the number is prime if no divisors are found up to the square root of the number.
- 555: This number ends in a 5, making it divisible by 5. Thus, it is a composite number.
- 313131: Since this number doesn't end with 0 or 5, it is not divisible by 5 and it doesn't display obvious divisibility by 2, 3, or any small prime numbers. It requires a deeper prime factorization check.
- 434343: This number also doesn't end with 0 or 5, so it's not divisible by 5 and doesn't show clear signs of divisibility by other small primes.
- 454545: Like 555, this number ends in 5, hence it is divisible by 5 and is a composite number.
- 535353: Once more, this number also ends in 3 which means we need to test for divisibility by other numbers aside from 2 and 5.
Through the method explained, we can determine that the numbers ending in 5, namely 555 and 454545, are composite because they are divisible by 5. Therefore, without further calculations, we know that at least Options A and D are composite numbers. Since only one answer can be correct and we are sure 555 is composite, we select Choice A (555) as the correct option.