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JEE Main 20203 SeptemberEvening Shift
Exam
JEE Main
Year
2020
Date
3 September
Shift
Evening Shift
Subject
Mathematics
Chapter
Probability

JEE Main 2020 · 3 September · Evening Shift · Mathematics · Probability

The probability that a randomly chosen 5 - digit number is made...

The probability that a randomly chosen 55- digit number is made from exactly two digits is :

Options

  1. A135104\dfrac{135}{{10}^{4}}
  2. B150104\dfrac{150}{{10}^{4}}
  3. C134104\dfrac{134}{{10}^{4}}
  4. D121104\dfrac{121}{{10}^{4}}

Correct answer

A. 135104\dfrac{135}{{10}^{4}}

Step-by-step solution

Total number of five-digit numbers are 9(104)9\left({10}^{4}\right).

Case I : Choosing two non-zero digits i.e. in C29C2 9 ways.

So, number of five-digit numbers containing both digits =25−2= {2}^{5} - 2.

Case II : Choose one non-zero and one zero as digit i.e. in C19C1 9 ways.

So, number of five-digit numbers containing one non-zero and one zero both =24−1= {2}^{4} - 1.

So, favourable number of ways =C29(25−2)+C19(24−1)=36(30)+9(15)=1080+135=1215= C2 9 \left({2}^{5} - 2\right) + C1 9 \left({2}^{4} - 1\right) = 36\left(30\right) + 9\left(15\right) = 1080 + 135 = 1215

Thus, required probability =12159×104=135104= \dfrac{1215}{9 \times {10}^{4}} = \dfrac{135}{{10}^{4}}.

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