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There are four prime numbers written in ascending order of magnitude. The product of the first three is 7429 and of the last three is 12673. Find the fourth number?

Correct answer: B. 29

  • A. 17
  • B. 29
  • C. 23
  • D. 31

Explanation

7429 = 17 x 19 x 23, so these are the first three primes. Since 12673 = 19 x 23 x 29, the fourth prime is 12673 ÷ (19 x 23) = 29. The likely mistake is option c, 23, which is the largest of the first three primes, not the fourth.

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