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.