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Unformatted text preview: Statistics 13A, Spring 2010, Midterm III Version B Name: ID: Instructions: 50 minutes, closed book midterm one lettersized (doublesided) cheatsheet, hand held calculator and scrap paper are allowed 20 multiple choice problems, 5 points each put your name & ID on this midterm and scantron hand in both this midterm and scantron (the midterm will be used as a proof of your presence in the un likely event of missing scantron) grading is based on scantron which will not be re turned to you this is Version B, please mark the corresponding circle on the scantran good luck! Midterm begins here... 1. Which of the following statements is true with re gards to the probability density functions of continu ous random variables ? (choose the most appropriate answer) (a) They are symmetrical (b) They are skewed to the left (c) They are skewed to the right (d) Their values are always in between 0 and 1 (e) The area under the curve is one 2. Let X be a continuous random variable and let a and b be two constants with a < b . Which of the follow ing statements is false ? (choose the most appropri ate answer) (a) The probability that X assumes a value in the interval ( a , b ) is the area under the probability density function between a and b (b) P ( X = a or b ) = (c) P ( X b ) = P ( X < b ) (d) P ( a < X < b ) = P ( X b ) P ( X a ) (e) None of the above 3. If Z is a standard normal random variable, then what is P ( Z  . 67 ) ? (choose the closest answer) (a) 0.15 (b) 0.25 (c) 0.50 (d) 0.65 (e) 0.75 4. If the random variable X has a normal distribution with mean and standard deviation , then P (  < X < + 2 ) is (choose the closest answer) (a) 0.002 (b) 0.159 (c) 0.819 (d) 0.841 (e) 0.977 5. Suppose that Z is a standard normal random variable. If P ( Z x ) > . 5 for a real number x , then which of the following is true with regards to the sign of x ? (a) x is negative (b) x is positive (c) x is zero (d) the probability that x is positive is 0 . 5 (e) not enough information to determine 6. Let z be the value such that the area under the stan dard normal curve to the left of z is 0.8485. Then the value of z is (a) 1 . 00 (b) 1 . 03 (c) 1.00 (d) 1.03 (e) . 03 7. The number of different samples of size n = 3 that one can obtain by sampling using simple random sampling without replacement from a population of N = 5 distinct elements is: (a) 3! (b) P 5 3 (c) C 5 3 (d) 5 3 (e) 3 5 8. In order to estimate the average number of miles that students who live offcampus commute to classes ev ery day, the following statistics were given : n = 74, x = 5 . 21 and s = 2 . 48. An estimate of the standard error of the sample mean is (a) 0.034 (b) 0.070 (c) 0.288 (d) 0.606 (e) 2.48 9. In a sample of 200 items, 14 items are defective. The point estimate of the population proportion of defec tive items is: (a) 0.07 (b) 0.14 (c) 7 (d) 14 (e) 42 10. A random sample of n = 50 observations from a quantitative population produced...
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 Spring '10
 samaniego
 Statistics

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