CUET · MATHS · PYQ PAPER 2023
On a multiple choice examination with 4 possible answers (out of which one is correct)
for each of the five questions, the probability that a candidatewould get 4 or more correct answers just by guessing is:
- A \(\frac{1}{64}\)
- B \(\frac{1}{256}\)
- C \(\frac{1}{16}\)
- D \(\frac{1}{4}\)
Answer & Solution
Correct Answer
(A) \(\frac{1}{64}\)
Step-by-step Solution
Detailed explanation
\(p = 1/4\), \(q = 3/4\), \(n = 5\) \(P(X=4) = C(5, 4) (1/4)^4 (3/4)^1 = 5 \cdot (1/256) \cdot (3/4) = 15/1024\) \(P(X=5) = C(5, 5) (1/4)^5 (3/4)^0 = 1 \cdot (1/1024) \cdot 1 = 1/1024\) \(P(X \ge 4) = P(X=4) + P(X=5) = 15/1024 + 1/1024 = 16/1024 = 1/64\)
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