In: Statistics and Probability
15) 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 240.52 seconds and the standard deviation is 94.47 seconds.
What is the upper bound for a 95% confidence interval for the actual mean length of the songs? Give your answer to 4 decimal places.
Your Answer:
Solution :
Given that,
Point estimate = sample mean =  
   = 240.52
Population standard deviation =   
= 94.47
Sample size n =45
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
Z
= Z0.05 = 1.645 ( Using z table )
Margin of error = E =   Z
/2   
* ( 
 /n)
= 1.645 * ( 94.47 / 45 
 )
= 23.1661
At 95% upper confidence interval population mean
is,
< 
 + E
< 240.52 + 23.1661
< 263.6861
Answer:263.6861