# Thread: Lower Limit and Upper Limit Confidence Levels

1. ## Lower Limit and Upper Limit Confidence Levels

I am having trouble with a set of homework questions revolving around upper and lower limit confidence levels. Here is an example of what I mean:

The mean diastolic blood pressure for a random sample of 80 people was 99 millimeters of mercury. If the standard deviation of individual blood pressure readings is known to be 11 millimeters of mercury, find a 99% confidence interval for the true mean diastolic blood pressure of all people. Then complete the table below.
Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.

What is the lower limit of the 99% confidence level?
What is the upper limit of the 99% confidence level?

I have read over the example problems but it is not sinking in.

Any help would be appreciated. Thanks!

2. Hello seahawk
beacuse of s.d is known (belongs to population),my reason is this term of u :
" If the standard deviation of individual blood pressure readings is known to be 11 millimeters of mercury"
so a 99&#37; confidence interval for the true mean diastolic blood pressure of all people is:

L= 99 _ Z(.95)*11

U= 99 + Z(.95)*11

Z(.95)=1.645

but if your intent in this term is not that s.d belongs to population
so instead of Z(.95), u must use t(.95) with 79 as degree of freedom.

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