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MHT CET · Maths · Probability

If \(X \sim B\left(8, \frac{1}{2}\right)\), then \(P(|x-4| \leq 2)=\)

  1. A \(\frac{119}{128}\)
  2. B \(\frac{29}{128}\)
  3. C \(\frac{238}{728}\)
  4. D \(\frac{119}{228}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{119}{128}\)

Step-by-step Solution

Detailed explanation

We have \(\mathrm{n}=8, \mathrm{p}=\frac{1}{2} \quad \Rightarrow \mathrm{q}=\frac{1}{2}\)
To find \(\mathrm{P}(|\mathrm{X}-4| \leq 2) \quad \Rightarrow \mathrm{X}=2,3,4,5,6\)
Hence required probability
\(={ }^{8} C_{2}\left(\frac{1}{2}\right)^{6}\left(\frac{1}{2}\right)^{2}+{ }^{8} C_{3}\left(\frac{1}{2}\right)^{5}\left(\frac{1}{2}\right)^{3}+{ }^{8} C_{4}\left(\frac{1}{2}\right)^{4}\) \(\left(\frac{1}{2}\right)^{4}+{}^{8} C_{5}\left(\frac{1}{2}\right)^{3}\left(\frac{1}{2}\right)^{5}+{ }^{8} C_{6}\left(\frac{1}{2}\right)^{2}\left(\frac{1}{2}\right)^{6} \)
\( =\left(\frac{1}{2}\right)^{8}\left[{ }^{8} C_{2}+{ }^{8} C_{3}+{ }^{8} C_{4}+{ }^{8} C_{5}+{ }^{8} C_{6}\right] \)
\( =\frac{1}{256}[28+56+70+56+28]=\frac{238}{256}=\frac{119}{128}\)