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Final

# STA 205 Lecture Notes - Lecture 10: Confidence IntervalExam

Department
Statistics
Course Code
STA 205
Professor
Brooke Buckley
Study Guide
Final

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12/17/2018 NKU Imath Assessment
https://imath.nku.edu/course/gb-viewasid.php?stu=11461&cid=335&asid=153573&uid=11461 1/8
Damico , Emily
Topic 10: Confidence Interval for the Mean
Started: November 8, 2018, 1:51 pm
Last change: November 8, 2018, 3:44 pm
Time spent: 112 minutes
Total time questions were on‑screen: 72.1 minutes.
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monitortheircaffeineintakeoverthecourseofoneday.Themeanamountofcaffeineconsumedinthe
sampleofwomenwas238.159mgwithastandarddeviationof203.245mg.Inthearticle,researcherswould
liketoincludea98%confidenceinterval.
Thevaluesbelowaretcriticalpointcorrespondingto90%,95%,98%,and99%confidence.Which
criticalpointcorrespondsto98%confidence?
2.02
2.421
2.701
1.683
With98%confidence,weestimatethemeanamountofcaffeineconsumedbywomenisbetween
mgand mg.(Roundthelimitsofyourintervalto4decimalplaces.)
Ifthelevelofconfidencewerechangedto90%,whateffectwouldthishaveonthewidthofthe
calculatedconfidenceinterval?
theintervalwouldnarrow
theintervalwouldwiden
therewouldbenoeffectontheinterval
Question 1: 8 (parts: 1.5, 2.5, 2.5, 1.5) out of 8 (parts: 1.5, 2.5, 2.5, 1.5)in 2 attempt(s)

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12/17/2018 NKU Imath Assessment
https://imath.nku.edu/course/gb-viewasid.php?stu=11461&cid=335&asid=153573&uid=11461 2/8
statisticiandecidedtoinvestigatefurther.Asampleof46flightsoriginatinginCincinnatiwasselected,and
theroundtripairfareforeachflightwasrecorded.ThesampledataissummarizedintheStatCrunchoutput
below:
With95%confidence,weestimatethemeanairfareforflightsoutofCincinnatiisbetween\$
and\$ .(Roundthelimitsofyourintervalto4decimalplaces.)
Themeanairfarenationwidewasreportedas\$376foraroundtripticket.Doestheintervalfound
abovesupporttheclaimthatCincinnatihasairfareswhicharemoreexpensivethanotherairportsin
theUS?
Theintervaldoesnotsupportthisclaimbecauseanairfareof\$376doesnotfallinsidethe
interval.
Theintervaldoesnotsupporttheclaimbecausetheentireintervalisnotabove\$376.
Theintervalsupportstheclaimbecausetheentireintervalisgreaterthan\$376.
Wecan'tmakethisconclusionbasedonaconfidenceinterval.
Youneedtoscheduleaflightforthesummer.Ifyouwanttoestimatethecostofyourflight,which
intervalwouldbemostappropriateforestimatingthecost?
theconfidenceinterval
anintervalbasedontheEmpiricalRuleorChebyshev'sRule(dependingontheshapeofthe
data)
Supposethesampleselectedwastakensothatthe46mostexpensiveflightsfromCVGwereselected.
Whichassumptionhasbeenviolated?
quantitativedata
randomsample
normality

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12/17/2018 NKU Imath Assessment
https://imath.nku.edu/course/gb-viewasid.php?stu=11461&cid=335&asid=153573&uid=11461 3/8
Question 2: 8 (parts: 2.5, 2.5, 1, 1, 1) out of 8 (parts: 2.5, 2.5, 1, 1, 1)in 1 attempt(s)
washtheirhandsperday.Themeannumberoftimesthosesampledwashedtheirhandswas8.908witha
standarddeviationof5.245.Researcherswouldliketoincludea90%confidenceinterval.
Howmanydegreesoffreedomwouldbeassociatedwiththetdistribution?df=
With90%confidence,weestimatethemeannumberoftimesanindividualwashestheirhandsis
between and .(Theappropriatetcriticalpointist=1.647.Roundthelimitsofyour
intervalto4decimalplaces.)
than9timesperday,onaverage?
Yes.Theintervalfallsentirelybelow9.
No.Theintervalextendsabove9.
Yes.Mostoftheintervalfallsbelow9.