latest edit: Tuesday, March 10, 01:20 pm
wostner: exercises: binomial distribution  2
©20062009 ulf wostner<[email protected]>
These problems can be solved using BINOMIAL(n,p) distribution. But, for practical reasons, in some of the
problems you will need to use an approximation:
BINOMIAL(n, p) ≈ NORMAL(μ, σ)
Recall that for X=BINOMIAL(n,p), we have E(X)=np, and SD(X)=√(npq)
1.
A multiplechoice test has 120 questions with four options on each question. Suppose you just
guess the answers.
a.
How many correct answers would you get, on average?
Answer: 30
b.
What is the standard deviation of the number of correct answers?
Answer: 4.74
c.
This is not Normal Distribution, but it comes close. According to the Rule of Thumb,
the probability is 95% that the number of correct answers falls into a certain interval.
Which interval?
Answer: 20.52 < X < 39.48
d.
P(at least 35 correct answers) =
Answer: 0.17
2.
You roll a die 240 times.
a.
On average, how many sixes will you get?
Answer: E(X)=40.0000
b.
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 Spring '09
 Wostner
 Math, Binomial, Normal Distribution, Standard Deviation

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