
(a)
The appropriate null and alternate hypotheses.
(a)

Answer to Problem 13E
Null hypothesis:
That is, the percentage of emails that are spam is not differs from
Alternative hypothesis:
That is. the percentage of emails that are spam differs from
Explanation of Solution
Given information:
According to Secure List,
A system manager suspects that the spam email percentage at his company may be
In an inspection he finds that
Calculation:
A system manager suspects that the spam email percentage at his company may be
So null and alternate hypotheses would be given as-
Null hypothesis:
That is, the percentage of emails that are spam is not differs from
Alternative hypothesis:
That is. the percentage of emails that are spam differs from
(b)
The test satistic
(b)

Answer to Problem 13E
Explanation of Solution
Given information:
Same as part
Formula used:
Calculation:
A system manager suspects that the spam email percentage at his company may be
i.e.
In an inspection it is found that
The value of
Calculating the test statistic
Thus, the value of test statistic
(c)
Whether the percentage of emails that are spam differs from
(c)

Answer to Problem 13E
It can be concluded that there is evidence at level of significance
Explanation of Solution
Given information:
According to Secure List,
A system manager suspects that the spam email percentage at his company may be
In an inspection he finds that
Concepts used:
From the two tailed test.
If
If
Calculation:
From part
From Table
From the two tailed test.
If
If
Since
Therefore the null hypothesis is rejected.
Hence, it can be concluded that there is evidence at level of significance
(d)
Whether the percentage of emails that are spam differs from
(d)

Answer to Problem 13E
It can be concluded that there is no evidence at level of significance
Explanation of Solution
Given information:
According to Secure List,
A system manager suspects that the spam email percentage at his company may be
In an inspection he finds that
Calculation:
From part
Since the test is two-tailed and level of significance
From Table
Rejection rule:
From the two-tailed test,
If
If
Conclusion for
The value of test statistic is
Here, the value test statistic lies between lower and upper critical value. Therefore, the null hypothesis is not rejected.
Hence, it can be concluded that there is no evidence at level of significance
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Chapter 9 Solutions
Elementary Statistics (Text Only)
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