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# Confidence interval for mean

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Find a confidence interval for mean assuming that each sample is from a normal population.
a. ¯x = 24, s = 3, n = 7, 90 percent confidence
b. ¯x = 42, s = 6, n = 18, 99 percent confidence
c. ¯x = 119, s = 14, n = 28, 95 percent confidence

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The solution finds Confidence interval for mean for 90%, 99% and 95% confidence.

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Find a confidence interval for mean assuming that each sample is from a normal population.
a. ¯x = 24, s = 3, n = 7, 90 percent confidence
b. ¯x = 42, s = 6, n = 18, 99 percent confidence
c. ¯x = 119, s = 14, n = 28, 95 percent confidence

a. ¯x = 24, s = 3, n = 7, 90 percent confidence

90% Confidence limits

Mean=M = 24
Standard deviation =s= 3
sample size=n= 7
sx=standard error of mean=s/square root of n= 1.1339 = ( 3 /square root of 7)
Confidence level= 90%
Therefore Significance level=alpha (a) = 10% =100% -90%
No of tails= 2
2 tails because we are calculating the confidence interval

Since sample size= 7 < 30
and we are using sample standard deviation to ...

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