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Unformatted text preview: MATH 220 7 TEST #2 NAME D0 WM?" 1": 5 SECTION c» SHOW YOUR WORK! HONOR PLEDGE: I have neither given nor received help from any person on this exam.
Signed l. Bigger animals tend to carry their young longer before birth. The length of horse
pregnancies from conception to birth varies according to a roughly normal distribution
with mean 336 days and standard deviation 3 days. What proportion of horse pregnancies last between 330 and 340 days? ‘ g {‘3 7
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wimp i'P‘dOan'éVﬂ/l 2. Final averages are typically approximately normally distributed with a mean of7f and a standard deviation of 12.5. Your professor says that the top 8% of the class will
receive an A. What average must you exceed to obtain an A? X 1 {girl WW \l 4 1w I”? H9?;‘,}&€ (H \‘L 6% 19:5 \ ' ' I“ 1 73\ £3 y *3? : 1 1“ (“1'59" +7‘1
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7; y ~ g‘lrb 3. In California, 30% of the people have a certain blood type. What is the probability that exactly 3 out of a randomly select group of 7 Californians will have that
blood type? V‘.‘ " {aii’irxrxfazxa ham Ethel "WW,
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ct Sit/'7'3li': ‘ 4. Four of the 20 students (20%) in a class are fraternity or sorority members. Five
students are picked at random. Does X = the number of students in the sample who are
fraternity or sorority members have the binomial distribution with n = 5 and p = 0.20?
Explain why or why not. , .4 ~ r .. ’ 4
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5. Suppose that 40% of adults are committed to eating nutritious food when eating away from home. You operate a restaurant. To help plan your menu, you decide to
conduct a sample survey in your area. You will use random digit dialing to contact a
simple random sample of 200 households by telephone. a. What is the mean number of nutritious conscious people in your sample?
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food when eating away? ‘  ‘ ‘r '7‘; :f‘ i
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6. Name the type of sample survey bias existing in the following: (p I ,1 fix}? ; $.32. a
a. “More than half of Califomia’s doctors say they are so frustrated with managed care they will quit, retire early, or leave within three years.” This statement was a lead
sentence in a newspaper article. This conclusion was based on a mail survey conductrd
by the California Medical Association. Surveys were mailed to a random sample of 5000
California doctors, and 500 cornpleted surveys were returned. N!) i‘; ~ rec{2:0 E: St: 3* riff;
b. Studies linking abnormal genes to an increased risk of breast cancer are now
being reevaluated. An article stated that “early studies that evaluated breast cance risk
among gene mutation carriers selected women in families where sisters, mothers, and
grandmothers all had breast cancer. This created a statistical bias that skewed risk estimates for women in the general population.” . r r
Eﬁmﬁfiaﬁ h' J 7. A pharmaceutical company has developed a new drug for treating high blood
pressure. They would like to compare its effects to those of the most popmﬁg
currently on the market. Two hundred volunteers with a history of high blood pressure
and who are currently not on medication are recruited to participate in a study. Half of
the volunteers will be randomly assigned the new drug and the other half the drug already
on the market. a. Identify the explanatory van'able and the response variable
if: . =~ “QM {cg d t" ‘u H {ail Jim tiara: Mel n 1‘ “ : "d .V y ,5“ 'cw.
RA L glen«i ftaggwa a)" fjﬁ'ofi m Mac/<3 i . b. Is this an observational study or an experiment. Explain. Be sure to put your
response in context of this example. 1
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c. What is the purpose of the randomizatlon? lee examples. { .15 , iii
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(if ﬂy'iit’wiaxia r d. Explain what would have to be done to make this study double—blind. p\ Vm‘ E341 (fr; Hle {Elite m odhﬂix‘ by“ ﬁlé'vq QTY—€1,315 1\ {Wit Carma: blﬂ’ﬁ‘flffW9'ﬁitjf‘a €51 Maura“.
do not Mam M5961 Qiacirriprc’fﬁare petriﬁed 4'5 Ffff’E/Et‘g 8. Find the zscore such that the interval within 2 standard deviations of the mean for
a normal distribution contains 60% of the probability. “ ~;:,x~ a a D. t’ Li" i — ’3: o ~2~
9. Let the random variable X be the number of cars (including SUVs and light
trucks) that American households own. The probability distribution for X is given belo‘ a." ,7: x 0 1 2 3 4 5
P(x) 0.09 0.36 0.35 0.13 0.05 0.02 , a
Show that the two conditions in the deﬁnition of a probability distribution are satisfied. a} y g\ the 0‘5 WA 1‘6: aft”; #1 "' ~.~ ‘’ .L, v r W \ J
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