In: Statistics and Probability
A survey of 29 sugar addicts showed that they eat 13 jumbo candy bars a week. If the trend follows a typical normal distribution with a standard deviation of 3 candy bars a week, find the 99% confidence interval for the true average amount of candy bars eaten per week.
solution
Given that,
= 13
s =3
n = 29
Degrees of freedom = df = n - 1 =29 - 1 =28
At 99% confidence level the t is ,
= 1 - 99% = 1 - 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
t /2,df= t0.005,28 = 2.763 ( using student t table)
Margin of error = E = t/2,df * (s /n)
= 2.763* (3 / 29) = 1.5392
The 99% confidence interval estimate of the population mean is,
- E < < + E
13 - 1.5392< < 13+ 1.5392
11.4608< <14.5392
11.4608,14.5392