answers to review w s
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Answers to Review WS (1-7)
Review for Ch 19 -22 TEST
WS #1
• Conditions are met. Be sure to write formulas and plug in to check.
• Formula for confidence interval:
Interval: (-.2146, .05462)
We are 90% confident that the difference in proportion
of those favoring the church proposal between the 25-
40 year age group and the 40 – 60 year age group is in
the interval -.21 to .05.
1 1 2 2*1 2
1 2
ˆ ˆ ˆ ˆ1 1ˆ ˆ
p p p pp p z
n n
WS #2
• Assumptions are met.
* (1 )p pME z
n
.83(.17)1.645 .0618
100ME
WS #3
* (1 )p pME z
n
.35(.65).03 1.96
972n
n
Notes: Always round up when reporting n.In this problem we had some idea what p should be. Many times we do not. If we don’t know then use 0.5 for p.
WS #4
ˆ.71
(1 )
.2386
p pz
p pn
p
: .45
: .45o
a
H p
H p
Fail to reject the null since p-value is greater than alpha = .05. There is no evidence to suggest that the proportion of freshmen placed on academic probabation is less than 45%.
p is proportion of freshmen placed on academic probation.
Assumptions are all met – be sure to write formulas and plug in values to check.
Be sure to write formula!
WS #5
• Assumptions not met. Sample size is too small for np>10
WS #6
1 2
1 2
:
:o
a
H p p
H p p
p1 is proportion of urban high school students who plan to pursue a post-secondary education.P2 is proportion of suburban high school students who plan to pursue a post-secondary education.
Conditions are met, be sure to list and check these!
1 2
1 2
ˆ ˆ
1 1ˆ ˆ1
p pz
p pn n
1 2
1 2
ˆx x
pn n
.214
.83
z
p
Fail to reject the null since p-val is > than alpha =.05.There is no evidence to suggest that the two proportions between urban and suburban high school students who plan to pursue a post-secondary education are different.
WS #7
: .25
: .25o
a
H p
H p
P is proportion of explosives found.
ˆ1.14
(1 )
.1265
p pz
p pn
p
All conditions are met. Be sure to list and check all conditions.
Fail to reject null since p-val is > alpha = .05. There is no significant evidence to suggest the hand held sensor finds explosives more than 25 percent of the time.
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