Question

In: Statistics and Probability

To test Upper H 0 ​: mu equals20 versus Upper H 1 ​: mu less than20​,...

To test Upper H 0 ​: mu equals20 versus Upper H 1 ​: mu less than20​, a simple random sample of size nequals 19 is obtained from a population that is known to be normally distributed. Answer parts​ (a)-(d).

(a) If x overbar = 18 and s= 4.2 ​, compute the test statistic. ​(Round to two decimal places as​ needed.)

​(b) Draw a​ t-distribution with the area that represents the​ P-value shaded. Which of the following graphs shows the correct shaded​ region?

​(c) Approximate the​ P-value.

​(d) If the researcher decides to test this hypothesis at the a= 0.05 level of​ significance, will the researcher reject the null​ hypothesis?

Solutions

Expert Solution

Solution:
The provided sample mean is x̄ = 18 and the known population standard deviation is

s = 4.2, and the sample size is n = 19.

Null and Alternative Hypotheses:
The following null and alternative hypotheses need to be tested:

Ho: μ = 20
Ha: μ < 20
This corresponds to a one tailed test, for which a t-test for one mean, with unknown population standard deviation will be used.

a) Test statistic:


t= -2.08

b) Area of p-value :



c)
Using the P-value approach: The p-value is p = 0.0263, ..using excel formula, =TDIST(2.08,18,1)

and since p = 0.0263< 0.05, it is concluded that the null hypothesis is rejected

d)Conclusion: It is concluded that the null hypothesis Ho is rejected. Therefore, there is enough evidence to claim that the population mean μ is less than 20, at the 0.05 significance level.


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