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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Probability

NDA 2019 · Mathematics · Probability

There are n socks in a drawer, of which 3 socks are red. If 2 of...

There are n socks in a drawer, of which 3 socks are red. If 2 of the socks are chosen randomly and the probability that both selected socks are red is 12\frac{1}{2}, then what is the value of n?\mathrm{n} ?

Options

  1. A3
  2. B4
  3. C5
  4. D6

Correct answer

B. 4

Step-by-step solution

Number of socks =n=\mathrm{n} Number of red socks =3=3 Given, 3C2nC2=12\frac{{ }^3 C_2}{{ }^n C_2}=\frac{1}{2}⇒nC2=3×2=6⇒n=4\begin{aligned} & \Rightarrow{ }^n C_2=3 \times 2=6 \\ & \Rightarrow n=4\end{aligned}$$
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