Question
Three integers are chosen at random from the first 20 integers. The probability that their product is even is,
  1. $\frac{2}{19}$
  2. $\frac{3}{29}$
  3. $\frac{17}{19}$
  4. $\frac{4}{19}$

Answer

  1. $\frac{17}{19}$

Soluction:

Required probability that product of two integers should be even.

10 integers are odd out of first 20 integers.

Required probability = 1 - Probability of product is odd

Product of three integers is odd if two numbers are odd

Required probability $=1-\frac{10}{20}\times\frac{9}{19}\times\frac{8}{18}=\frac{17}{19}$

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