In: Statistics and Probability
iTunes songs ~ iTunes library of mp3s has a very large number of songs. A student creates a playlist of 45 randomly selected songs. The sample mean length of the songs is 240.14 seconds and the standard deviation is 92.34 seconds.
Note: Numbers are randomized in each instance of this question. Pay attention to the numbers in this question.
What is the lower bound for a 95% confidence interval for the actual mean length of the songs? Give your answer to 4 decimal places.
Given that,
= 240.14
s = 92.34
n = 45
Degrees of freedom = df = n - 1 = 45 - 1 = 44
At 95% confidence level the t is ,
= 1 - 95% = 1 - 0.95 = 0.05
t,df = t0.05,44 = 1.680
Margin of error = E = t,df * (s /n)
= 1.680 * (92.34 / 45)
= 23.1256
The 95% confidence interval estimate of the population mean is,
- E < < + E
240.14 - 23.1256 < < 240.14 + 23.1256
217.0144 < < 237.2656
Lower bound = 217.0144