Question

a random sample of 13 students were asked how long it took them to complete a certain exam. The mean length of time was 122.1 minutes what the standard deviation of 66.6 minutes. Final lower bound of 90% confidence interval for the true mean length of time it would take for all students to complete the exam . Round to one decimal place

Answer #1

Solution :

Given that,

Point estimate = sample mean = = 122.1

sample standard deviation = s = 66.6

sample size = n = 13

Degrees of freedom = df = n - 1 = 13 - 1 = 12

At 90% confidence level the t is ,

t = 1 - 90% = 1 - 0.90 = 0.1

t,df = t0.1,12 = 1.356

Margin of error = E = t,df * (s /n)

= 1.356 * (66.6 / 13)

= 25.0

At 90% lower confidence level is

- E

122.1 - 25.0

97.1

lower bound is **97.1**

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