Using the Excel sheet for Cons
Using the Excel sheet for Constructing Confidence Intervals,answer the following questions.
1. Construct a 90% confidence interval for the truemean of a normal population if a random sample size of 40 from thepopulation yields a sample mean of 75 and the population has astandard deviation of 5.
Lower limit: ______________ upper limit:______________
2. A random sample, consisting of the values listed below, wastaken from a normally distributed population. Assuming the standarddeviation of the population is unknown, construct a 99% confidenceinterval for the population mean.
Table for 2 |
|||
27.4 |
26.5 |
25.7 |
31.4 |
28.2 |
21.9 |
16.3 |
22.7 |
18.8 |
34.4 |
29.2 |
20.5 |
Lower limit: ______________ upper limit:______________
Answer:
1)
Sample size = n = 40
Sample mean = = 75
Population standard deviation = = 5
We have to construct 90% confidenc interval for the populationmean.
Here population standard deviation is known so we have to useone sample z-confidence interval.
z confidence interval
Here E is a margin of error
Zc = 1.645 ( Using z table)
So confidence interval is ( 75 – 1.3004 , 75 + 1.3004) = >( 73.6996 , 76.3004)
Using excel
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