Download Handwritten Notes on Confidence Intervals - Intro to Statistics | STAT 1222 and more Study notes Statistics in PDF only on Docsity! 4
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4. A NAPA Auto Parts supplier wants to get information about the number of ‘8 car owners keep their
cars. A random sample of 25 car owners resulted in & = 7.01 years, and ‘4 years, Assume that
the sample is drawn from a normally distributed population. Construct a 95% confidence interval for
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5. In arandom sample of 20 people with advanced degrees in biology, the mean monthly income was $4744
and the standard deviation was $580. Assume the monthly incomes are Rormally distributed.
(a) Construct a 99% confidence interval for the mean monthly income for people with advanc ‘ed degrees
in biology. é
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(b) Suppose that the population standard deviation is reported to be $580. Construct a 99% confidence
interval for the mean monthly income in the above.
Homework 5
Stat 1222-011 (Professor: Dr. A. Biswas)
NCS eer ID#:
1. Find the z-score satisfying the given conditions below.
(a) (1 pts) The z-score has 80% of the distributions area to the left.
Answer:
(b) (1 pts) The =
Answer:
{c} (2 pts} 75% of the distributions area lie between —z and z.
Answer:
core has $5 % of the distributions area te the right.
Due: 3/03/09 (Tue)
2. The common final exam scores in statistics 1222 in a certain year were normally distributed with a mean
of 75 and a standard deviation of 10, Show work on (a) and (b) below
(a} (% pts} What is the smallest score that a student can receive and still be in the top five percent?
{b) (3 pts) If the bottom 23 % of the class receive a failing grade, what is the minimum score required
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by a student to pass the course? yo 26 go ~ ip
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3. An automobile insurer has found that repair claims have a mean of $ 920 and a standard deviation of $
70.
(a) (2 pts) The mean and standard deviation of the sample mean # of 100 claims chosen at random is
(i) mean = $920 and standard deviation = $ 87. ii) mean = $920 and standard deviation =
$ 8.70. mean = $92 and standard deviation = $ 87. {iv) mean = $92 and standard
deviation = § 870. (¥) none of the above.
(b) (4 pts) The probability thaefa yandomly ‘ chosen claim is larger than $1000 is
4) 0.4641 ii) 0.1788. tii} 0.8212. iv) 5859 ——v) none of these.
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(c) (4 pts) The probability that the sample mean # of the 100 claims is larger than $ 1000 is
(i) 0.1788. (i).:0.8212. (ii) 0.9200. iv) 0.0800.) .0228 ae ,
