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CMA Foundation · Fundamentals of Business Mathematics and Statistics · Set Theory, including Venn Diagram

Which of the following sets is a singleton set?

The set of natural numbers strictly between 3 and 5 contains only 4, so it is a singleton. The integer solutions of x² = 9 are two numbers, the natural numbers below 1 are none, and the primes between 10 and 20 are four.

  1. A{x : x is an integer and x² = 9}
  2. B{x : x is a natural number and 3 < x < 5}Correct
  3. C{x : x is a natural number and x < 1}
  4. D{x : x is a prime number and 10 < x < 20}

Explanation

For the second set, the only natural number between 3 and 5 is 4, so it has exactly one element. The first set is {-3, 3}, the third is empty, and the fourth is {11, 13, 17, 19}.

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