PART I. HYPOTHESIS TESTING
PROBLEM 1 A certain brand of fluorescent light tube was advertised as having an effective
life span before burning out of 4000 hours.
A random sample of 84 bulbs was burned out
with a mean illumination life span of 1870 hours and with a sample standard deviation of 90
hours.
Construct a 95 confidence interval based on this sample and be sure to
interpret this interval.
Answer
Since population standard deviation is unknown, t distribution can be used construct the confidence
interval.
The 95% confidence interval is given by
/2,
1
/2,
1
,
n
n
S
S
X
t
X
t
n
n
Details
Confidence Interval Estimate for the Mean
Data
Sample Standard Deviation
90
Sample Mean
1870
Sample Size
84
Confidence Level
95%
Intermediate Calculations
Standard Error of the Mean
9.819805061
Degrees of Freedom
83
t
Value
1.988959743
Interval Half Width
19.53119695
Confidence Interval
Interval Lower Limit
1850.47
Interval Upper Limit
1889.53

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