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Out of first 20 natural numbers, one number is selected at random. The probability that it is either an even number or a prime number is_____________?

Correct answer: D. 17/20

  • A. 1/2
  • B. 16/19
  • C. 4/5
  • D. 17/20

Explanation

Among 1 to 20, there are 10 even numbers and 8 primes: 2, 3, 5, 7, 11, 13, 17 and 19. Since 2 is counted in both groups, the favourable count is 10 + 8 - 1 = 17, giving 17/20. The likely mistake is choosing 4/5 by incorrectly treating 2 as an overlap to subtract without checking the resulting count, or by counting only 16 favourable numbers.

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