Confidence Intervals using Normal Distribution with variance known From

Sanai Huerta

Sanai Huerta

Answered question

2022-03-27

Confidence Intervals using Normal Distribution with variance known
From a sample of 32 observations from a population with σ2=24.602, we obtained x=79.47. Construct a 99% confidence interval for μ.
(a)79.47±1.4424
(b)79.47±1.7186
(c)79.47±2.0430
(d)79.47±2.2622

Answer & Explanation

kaosimqu5t

kaosimqu5t

Beginner2022-03-28Added 10 answers

Respectively, answers (A) through (D) correspond to symmetric two-sided 90%, 95%, 98%, and 99% confidence intervals. The critical values for each are:
a) 1.64485
b) 1.95996
c) 2.32635
d) 2.57583
with standard errors being 24.602320.87682. Thus the respective margins of error are (±).
(A) 1.44224, (B) 1.71853, (C) 2.03979, (D) 2.25854.
pautmndu

pautmndu

Beginner2022-03-29Added 10 answers

n=32
σ=4.96
SE=σn
ME=q.995SE
x=79.47
x+c(ME,ME)
=(77.21,81.73) Answer D
With some further explanation, I am certain the book made an error
Here is what the book used. They used a 95% confidence interval
n=32
σ=4.96
SE=σn
ME=q.995SE
x=79.47
x+c(ME,ME)
=(77.75,81.19)
You were right, the answer is in fact D. Hopefully the code isn't overwhelming, I could have done the same process by hand, but the book used z=1.96 for a 95% confidence interval, rather than using 2.58 for a 99% confidence interval

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