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NDA 2023
Exam
NDA
Year
2023
Subject
Mathematics
Chapter
Probability

NDA 2023 · Mathematics · Probability

Two distinct natural numbers from 1 to 9 are picked at random. What...

Two distinct natural numbers from 1 to 9 are picked at random. What is the probability that their product has 1 in its unit place?

Options

  1. A181\frac{1}{81}
  2. B172\frac{1}{72}
  3. C118\frac{1}{18}
  4. D136\frac{1}{36}

Correct answer

D. 136\frac{1}{36}

Step-by-step solution

There are only two combination are possible (3,7)(3,7), (7,3)(7,3) such that their product has 1 in its unit place. So, required probability =29×8=136=\frac{2}{9 \times 8}=\frac{1}{36}
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