MCQ
Mark the correct alternative in the following question : The probability of guessing correctly at least $8$ out of $10$ answers of a true false type examination is :
  • A
    $\frac{7}{64}$
  • $\frac{7}{128}$
  • C
    $\frac{45}{1024}$
  • D
    $\frac{7}{41}$

Answer

Correct option: B.
$\frac{7}{128}$
$\text{n}=10,\text{p = q}=\frac{1}{2}$
$\text{P(X}\geq8)=\text{P(8) + P(9) + P(10)}$
$\text{P(X}\geq8)=\text{ }^{10}\text{C}_8\big(\frac{1}{2}\big)^{10}+\text{ }^{10}\text{C}_{9}\big(\frac{1}{2}\big)^{10}+\text{ }^{10}\text{C}_{10}\big(\frac{1}{2}\big)^{10}$
$\text{P(X}\geq8)=\frac{45+10+1}{2^8}$
$\text{P(X}\geq8)=\frac{56}{256}=\frac{7}{128}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free