Multiple choice general knowledge math & puzzles

5) If both x and y are prime numbers, which of the following CANNOT be the difference of x and y?

  1. 1

  2. 23

  3. 3

  4. 15

  5. 9
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B Correct answer
Explanation

If x and y are prime, their difference can be 1 (3-2) or 3 (5-2). It can be 15 (17-2) or 9 (11-2). However, for a difference to be 23, one number must be even (2) and the other 25, which is not prime. If both are odd, the difference must be even.

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