Question

Suppose we gather the following sample: 40, 30, 11, 26, 41, 33, 28, 10, 30, 48

a) Using this sample, calculate the UPPER bond for the 95% confidence interval.

b) Using this sample, calculate the LOWER bound for the 95% confidence interval.

Answer 1

a) 95% confidence interval for mean is

where

degrees of freedom = n-1= 10-1 =9

For 95% confidence () , df =9 , critical value of t is

tc = 2.26 ( from t table)

Thus

Upper bound for 95% confidence interval is

=

=29.7+8.7012

= 38.401

(b)

Lower bound for 95% confidence interval is

=

=29.7-8.7012

= 20.999

Calculation :

	x	(x-xbar)^2
	40	106.09
	30	0.09
	11	349.69
	26	13.69
	41	127.69
	33	10.89
	28	2.89
	10	388.09
	30	0.09
	48	334.89
sum/ss	297	1334.1
xbar=sum/10	29.7
s^2=ss/9		148.233333
s		12.1751112