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NDA 2 2025 Maths, question 113

Topic: Probability

Q113

An integer is chosen at random from the first 5050 integers. What is the probability that the integer is neither divisible by 55 nor 99?

  1. (a) 7/107/10
  2. (b) 18/2518/25Correct answer
  3. (c) 37/5037/50
  4. (d) 19/2519/25

Solution.

Answer: (b) 18/2518/25

  1. Among 1 to 50 there are 10 multiples of 5, 5 multiples of 9, and 1 common multiple (45).
  2. Thus 14 are divisible by at least one.
  3. The remaining 36 give probability 36/50=18/25.