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math80.sample quiz10 - latest edit Tuesday:20 pm wostner...

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latest edit: Tuesday, March 10, 01:20 pm wostner: exercises: binomial distribution - 2 ©2006-2009 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 multiple-choice 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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