Question

the national program planner for the girl scouts wants to estimate

The national program planner for the Girl Scouts wants to estimate the average number of girls per troop. A random sample of 81 troops shows sample mean x = 14.8 girls with standard deviation 9.0 girls. Find a 99% confidence interval for the population mean number of girls per troop.

Answer 1

Here, n = 81

sample mean , $\overline{x}$ = 14.8 and standard deviation , s = 9

degrees of freedom =n-1 = 80

For 99% confidence level and df= 80 , t = 2.64

The confidence interval is =  $\overline{x}$$\pm$ t*s/$\sqrt$n

= 14.8  $\pm$ 2.639

= (12.161 , 17.439)