Which of the following statements is true about 63 and 20?

They are both prime numbers.
They have more than one common factor.
They are relatively prime.
They each have a factor of 4.

1 answer

Let's analyze the statements one by one regarding the numbers 63 and 20:

  1. They are both prime numbers.

    • This statement is false. A prime number has exactly two distinct positive divisors: 1 and itself.
    • 63 is not a prime number because it can be divided by 1, 3, 7, 9, 21, and 63.
    • 20 is not a prime number either since it can be divided by 1, 2, 4, 5, 10, and 20.
  2. They have more than one common factor.

    • This statement is false. The common factors of 63 and 20 are only 1. Since 1 is the only common factor, they do not have more than one common factor.
  3. They are relatively prime.

    • This statement is true. Two numbers are relatively prime if their greatest common divisor (GCD) is 1. Since the only common factor is 1, 63 and 20 are relatively prime.
  4. They each have a factor of 4.

    • This statement is false. While 20 has a factor of 4 (since 20 = 4 × 5), 63 does not (since 63 is not divisible by 4).

Based on the analysis, the correct statement is: They are relatively prime.