mental block, hypothesis testing

[jgrandits]

perhaps someone could shed some light on hypothesis testing and how they approach the following type of problem, fitting question because my IQ for hyp testing might be < 100, thanks.
In order to test if the mean IQ of employees in an organization is greater than 100, a sample of 30 employees is taken and the sample value of the computed test statistic, tn-1 = 1.2. If you choose a 5% significance level you should:
A) reject the null hypothesis and conclude that the population mean is greater than 100.
B) fail to reject the null hypothesis and conclude that the population mean is greater than 100.
C) fail to reject the null hypothesis and conclude that the population mean is not greater than 100.
Your answer: A was incorrect. The correct answer was C) fail to reject the null hypothesis and conclude that the population mean is not greater than 100.
At a 5% significance level, the critical t-statistic using the Student’s t distribution table for a one-tailed test and 29 degrees of freedom (sample size of 30 less 1) is 1.699 (with a large sample size the critical z-statistic of 1.645 may be used). Because the critical t-statistic is greater than the calculated t-statistic, meaning that the calculated t-statistic is not in the rejection range, we fail to reject the null hypothesis and we conclude that the population mean is not significantly greater than 100

 

[kh.asif]

1.
Null:IQ<=100
Alternate:IQ>100
2.
The decision rule is
If calculated t-statisitic>Critical Value reject null.
3.
Calculated=1.2
Critical (Using Table@5% significance and 29 degrees of freedom)=1.699
4.
So calculated is less that critical meaning that we fail to reject the Null. So we conclude that the IQ is not greater than 100.
I think you got the decision rule jumbled up.

 

[nicob]

join the group. i hate this stuff.
i would have used a z-statistic (because sample 30, but t-stat ok as sample small), standardised, checked the z-table and rejected as suited.
remember that it is the alternative hypothisis that we want to accept, the null we reject. Thus because you want to know the mean >100, the null hypoth would be <= 100, alt >100.
This last part i think is the most important part. Once you know the null/alt hypoth, your half way there.