Find the probability: A 10-question multiple choice test has 4 possible answers
for each question. A student guesses on all ten answer. What is the
probability that the student selects at least 6 correct answers?
A.) 0.995 B.) 0.020 C.)0.118 D.) 0.989
There are two ways to do it. You can either interpret this as
1. One minus the probability that the student will guess 5 or fewer
correct answers with a probability of a correct answer being :
1 - binomcdf(10,1/4,5) on your TI-83 or 84
Answer 0.0197277069
or
2. The probability that the student will guess 4 or fewer wrong answers
with a probability of a wrong answer being .
binomcdf(10,3/4,4)
Answer 0.0197277069
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Either way it rounds to 0.020, choice (B).
That means if the student guesses, the student only has 2 chances
out of 100, or 1 chance in 50, of passing with a D or better by guessing.
Edwin