Math Problem Statement

Select the value for x that is a counterexample to the following statement: If x is an integer that is greater than 20 and composite, then x is evenly divisible by 3.

Solution

The question asks for a counterexample to the statement:

"If xx is an integer that is greater than 20 and composite, then xx is evenly divisible by 3."

We need to find an integer xx from the given options that:

  1. Is greater than 20,
  2. Is composite (not prime), and
  3. Is not divisible by 3.

Let's evaluate each option:

  • Option A: x=23x = 23

    • 23 is greater than 20, but it is a prime number, not composite. So, it doesn't satisfy the composite condition.
  • Option B: x=27x = 27

    • 27 is greater than 20, and it is composite (27=3327 = 3^3).
    • It is divisible by 3, so it satisfies the statement. Not a counterexample.
  • Option C: x=10x = 10

    • 10 is composite (10=2×510 = 2 \times 5) but not greater than 20. So, this does not fit the conditions.
  • Option D: x=25x = 25

    • 25 is greater than 20, and it is composite (25=5225 = 5^2).
    • 25 is not divisible by 3, so this is a counterexample.

Conclusion:

The correct answer is D: x=25x = 25, as it satisfies the conditions for being a counterexample.

Would you like more details on the reasoning? Here are some related questions:

  1. What does it mean for a number to be composite?
  2. Why are composite numbers important in this context?
  3. Can prime numbers be counterexamples in such statements?
  4. How do you test if a number is divisible by 3?
  5. Can you give other examples of composite numbers greater than 20 that are not divisible by 3?

Tip: A composite number has more than two distinct factors, unlike a prime number which has only 1 and itself as divisors.

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Math Problem Analysis

Mathematical Concepts

Composite Numbers
Divisibility

Formulas

Divisibility rule by 3

Theorems

Definition of Composite Numbers

Suitable Grade Level

Grades 7-9