A telecommunications company wants to estimate the mean leng

A telecommunications company wants to estimate the mean length of time (in minutes) that 18 to 24 year olds spend text messaging each day.In a random sample of twenty seven 18 to 24 year olds, the mean length of time spent texting was 29 minutes.From past studies the is 4.5 minutes. Find the 90% confidence interval. Write the same steps as shown in #3.

Solution

Confidence Interval
CI = x ± Z a/2 * (sd/ Sqrt(n))
Where,
x = Mean
sd = Standard Deviation
a = 1 - (Confidence Level/100)
Za/2 = Z-table value
CI = Confidence Interval
Mean(x)=29
Standard deviation( sd )=4.5
Sample Size(n)=27
Confidence Interval = [ 29 ± Z a/2 ( 4.5/ Sqrt ( 27) ) ]
= [ 29 - 1.64 * (0.866) , 29 + 1.64 * (0.866) ]
= [ 27.5797,30.4203 ]