Question

A bank randomly selected 252 checking account customers and
found that 113 of them also had savings accounts at this same bank.
Construct a 90% confidence interval for the true proportion of
checking account customers who also have savings accounts.
**(Give your answers correct to three decimal
places.)**

Lower Limit -

Upper Limit -

Answer #1

The general formula for a confidence interval, the confidence interval for a true proportion, is:

**p ± z σ _{p}**

where **p** is the proportion in the sample,
**z** depends on the level of confidence desired, and
**σ _{p}** is the standard error of a
proportion, given by

where n is the sample size.

In this context:

Sample proportion

(level of significance)

( from the table )

90% confidence interval for the true proportion is :

**p ± z _{0.1} σ_{p}**

_{}**0.448±
1.64*0.0308**

_{}**0.448±
0.0505**

Lower Limit - 0.448- 0.0505 = 0.3975 **= 0.400**
(three decimal places)

Upper Limit - 0.448+ 0.0505 = 0.4985 **= 0.500**
(three decimal places)

a) A bank randomly selected 250 checking
account customers and found that 113 of them also had savings
accounts at this same bank. Construct a 95% confidence interval for
the true proportion of checking account customers who also have
savings accounts. (Give your answers correct to three
decimal places.)
Upper Limit -
Lower Limit -
b) In a sample of 50 randomly selected
students, 29 favored the amount being budgeted for next year's
intramural and interscholastic sports. Construct a 95%...

A savings and loan association needs information concerning the
checking account balances of its local customers. A random sample
of 14 accounts was checked and yielded a mean balance of $664.14
with a standard deviation of $297.29. Find a 90% confidence
interval for the true mean checking account balance for local
customers. Assume the variable is normally distributed. Give the
lower limit of the confidence interval as your answer below. Round
to two decimal places.

The First National Bank of Wilson has 600 checking account
customers. A recent sample of 60 of these customers showed 35 have
a Visa card with the bank? Construct the 90% confidence interval
for the proportion of checking account customers who have a Visa
card with the bank.

The First National
Bank of Wilson has 680 checking account customers. A recent sample
of 40 of these customers showed 27 have a Visa card with the
bank.
Construct the 90% confidence interval for the proportion of
checking account customers who have a Visa card with the bank. (Use
z Distribution Table.) (Round your answers to 3
decimal places.)

The First National Bank of Wilson has 680 checking account
customers. A recent sample of 60 of these customers showed 21 have
a Visa card with the bank.
Construct the 90% confidence interval for the proportion of
checking account customers who have a Visa card with the bank. (Use
z Distribution Table.) (Round your answers to 3
decimal places.)

The First National Bank of Wilson has 660 checking account
customers. A recent sample of 60 of these customers showed 35 have
a Visa card with the bank. Construct the 99% confidence interval
for the proportion of checking account customers who have a Visa
card with the bank. (Use z Distribution Table.) (Round your answers
to 3 decimal places.)
Confidence interval for the
proportion is between
and

The First National Bank of Wilson has 720 checking account
customers. A recent sample of 60 of these customers showed 22 have
a Visa card with the bank.
Construct the 98% confidence interval for the proportion of
checking account customers who have a Visa card with the bank. (Use
z Distribution Table.) (Round your answers to 3 decimal
places.)
Confidence interval for the proportion is between and
.

Wachovia Bank has 800 checking account customers. A recent
sample of 60 of these showed 35 to have a Visa card with the
bank.
Construct the 99% confidence interval for the proportion of
checking account customers who have a Visa with the bank.
b. What sample size would be needed if you want the estimated
proportion to be within 4% of the population proportion at the 99%
confidence level?
if possible draw distributions?
Thanks in advance

The First National Bank of Wilson has 660 checking account
customers. A recent sample of 50 of these customers showed 28 have
a Visa card with the bank. Construct the 98% confidence interval
for the proportion of checking account customers who have a Visa
card with the bank. (Use z Distribution Table.) (Round your answers
to 3 decimal places.)

The First National Bank of Wilson has 740 checking account
customers. A recent sample of 50 of these customers showed 27 have
a Visa card with the bank.
Construct the 99% confidence interval for the proportion of
checking account customers who have a Visa card with the bank. (Use
z Distribution Table.) (Round your answers to 3 decimal
places.)

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