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Press the STAT key.
Press the ► key twice to highlight TESTS.
Press the number 2 key.
Move the cursor over Stats and press the ENTER key.
Type in 50352 for µ
0.
Type in 51750 for Ë.
Type in 5240 for Sx.
Type in 200 for n.
Move the cursor over >µ
0
and press the ENTER key.
Move the cursor over Calculate and press the ENTER key.
The T-Test output shows the
alternative hypothesis: µ>50352
test statistic: t=3.77303543
p-value: 1.0635428E
-4
sample mean: Ë=51750
sample standard deviation: Sx=5240
sample size: n=200
The p-value is 1.064×10
−4
which is less than 1%. We reject H
0
and conclude that the average
salary of this year’s computer science graduates is statistically-significantly higher than $50,352.
Example: Auto Batteries
Grand Auto Corporation produces auto batteries. The company claims that its top-of-the-line
Never Die batteries are good, on average, for at least 65 months. A consumer protection agency
tested 15 such batteries to check this claim. It found the mean life of these 15 batteries to be 63
months with a standard deviation of 2 months. At the 5% significance level, can you conclude
that the claim of the company is true? Assume that the life of such a battery has an
approximately normal distribution.
Our hypotheses are H
0
: µ = 65 and H
1
: µ < 65. We will use the T-Test, choosing Stats, with
µ
0
= 65, Ë = 63, Sx = 2, n = 15, and µ
1
< µ
0
for our alternative hypothesis.
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