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Unformatted text preview: Statistics 13A, Spring 2010, Midterm III Version B Name: ID: Instructions: 50 minutes, closed book midterm one letter-sized (double-sided) cheat-sheet, 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 off-campus 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