Question

In: Statistics and Probability

A study investigated the compressive strength of concrete when mixed with fly ash.Nine random samples were...

A study investigated the compressive strength of concrete when mixed with fly ash.Nine random samples were taken.The population variance is unknown and assumed normal. The sample mean compressive strength x̅ = 25.12 psi and the sample standard deviation s = 8.42 psi.

Find a 99% lower one-sided confidence interval on mean compressive strength.

Expert Solution

Given that :

sample mean :

sample standard deviation :

sample size :

As population variance is unknown we need to use the t-interval formula .

The formula for lower one sided confidence interval for mean is ,

degrees of freedom = n - 1 = 9-1 = 8

df = 8

we need to find 99% lower one sided confidence interval ,

so c = 0.99

Excel gives critical value for two tailed ( that is for )

Using Excel function ,

Now plug the values in the formula ,

Therefore the 99% lower one-sided confidence interval on mean compressive strength is

orchestra answered 2 years ago

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