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NDA 2022 Maths · Mathematics · Probability · medium

A number is chosen at random from 1,2,…,30. The probability that it is a multiple of 4 or 6 is

Single correct option

A number is chosen at random from 1,2,…,301,2,\dots,30. The probability that it is a multiple of 44 or 66 is
  1. A. 415\dfrac{4}{15}
  2. B. 25\dfrac25
  3. C. 13\dfrac13
  4. D. 25+130\dfrac{2}{5}+\dfrac{1}{30}
Show answer and solution

Answer: (C) 13\dfrac13

Multiples of 44: 77; of 66: 55; of both (i.e. of 1212): 22. Count =7+5−2=10=7+5-2=10, probability 1030=13\frac{10}{30}=\frac13. Without subtracting the overlap you get 1230=25\frac{12}{30}=\frac25.
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Original question written in the NDA 2022 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake