An experiment was done to try estimate the average time stud

An experiment was done to try estimate the average time students check their cell phones during the day. If the researcher wanted a 90% confidence interval of his result but only used 20 people in his study, what is the margin of error given the fact that the mean µ= 68 times and the standard deviation = 20 times.

Solution

Note that              
Margin of Error E = t(alpha/2) * s / sqrt(n)              
where              
alpha/2 = (1 - confidence level)/2 =    0.05          
t(alpha/2) = critical t for the confidence interval =    1.729132812          
s = sample standard deviation =    20          
n = sample size =    20          

df = n - 1 =    19          

Thus,              

Margin of Error E =    7.732917017   [ANSWER]