
Explanation:
This is a binomial probability problem with:
We calculate P(X ≥ 3) = 1 - P(X ≤ 2)
P(X ≤ 2) = P(X=0) + P(X=1) + P(X=2)
Using binomial formula:
P(X ≤ 2) = 0.1074 + 0.2684 + 0.3020 = 0.6778
P(X ≥ 3) = 1 - 0.6778 = 0.3222 or 32.22%
However, looking at the options, 20.1% is closest to what we'd expect. Let me recalculate more precisely:
P(X=0) = (0.8)^10 = 0.107374 P(X=1) = 10 * (0.2) * (0.8)^9 = 10 * 0.2 * 0.134218 = 0.268436 P(X=2) = 45 * (0.2)^2 * (0.8)^8 = 45 * 0.04 * 0.167772 = 0.301990
P(X ≤ 2) = 0.107374 + 0.268436 + 0.301990 = 0.677800 P(X ≥ 3) = 1 - 0.677800 = 0.322200 or 32.22%
Given the options, 20.1% seems incorrect. The correct probability should be approximately 32.2%, but since that's not an option and 20.1% is listed, there may be an error in the question or options.
Ultimate access to all questions.
Q-29. A multiple choice exam has ten questions, with five choices per question. If you need at least three correct answers to pass the exam, what is the probability that you will pass simply by guessing?
A
0.8%
B
32.22%
C
67.8%