Question

A random sample of 13 size AA batteries for toys yield a mean of 2.82 hours with standard deviation, 0.84 hours.

(a) Find the critical value, t*, for a 99% CI. t* =

(b) Find the margin of error for a 99% CI.

Answer 1

Solution :

Given that,

= 2.82

s = 0.84

n = 13

Degrees of freedom = df = n - 1 = 13- 1 = 12

(A)

At 99% confidence level the t is ,

= 1 - 99% = 1 - 0.99 = 0.01

/ 2 = 0.01 / 2 = 0.005

_{t /2  df} = t_0.005,12 = 3.054

(b)Margin of error = E = t_/2,df * (s /n)   

E = 3.054 * ( 0.84/ 13) = 0.71