In: Statistics and Probability
If n=30, ¯xx¯(x-bar)=48, and s=3, find the margin of error at a
90% confidence level
Give your answer to two decimal places.
Solution:
Note that, Population standard deviation()
is unknown..So we use t distribution.
Confidence level = 90%
c = 0.90
= 1- c = 1- 0.90 = 0.10
/2
= 0.10
2 = 0.05
Also, d.f = n - 1 = 30 - 1= 29
=
=
0.05,29
= 1.699
( use t table or t calculator to find this value..)
The margin of error is given by
E = /2,d.f.
* (
/
n)
= 1.699 * (3 /
30)
= 0.93
margin of error = 0.93