3)
Assuming that the population of the study has a normal distribution and that you are studying the population mean μ.
The statistic hypotheses are
![\begin{gathered} H_0\colon\mu=87.8 \\ H_1\colon\mu](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20H_0%5Ccolon%5Cmu%3D87.8%20%5C%5C%20H_1%5Ccolon%5Cmu%3C87.8%20%5Cend%7Bgathered%7D)
If you look at the alternative hypotheses, it includes the symbol "<", which indicates that the test is <em>one-tailed</em>. This means that you will reject the null hypotheses at small values of the test statistic.
Since the sample size is small (n=4) and the given sample data. The test statistic to use for the test is the Student's t:
![t=\frac{\bar{X}-\mu}{\frac{S}{\sqrt[]{n}}}\sim t_{n-1}](https://tex.z-dn.net/?f=t%3D%5Cfrac%7B%5Cbar%7BX%7D-%5Cmu%7D%7B%5Cfrac%7BS%7D%7B%5Csqrt%5B%5D%7Bn%7D%7D%7D%5Csim%20t_%7Bn-1%7D)
To calculate the value of the statistic under the null hypothesis you have to use the sample data and the value of the population mean under the null hypothesis:
μ= 87.8
sample mean= 75
sample standard deviation= 17.1
n=4
![\begin{gathered} t_{H0}=\frac{75-87.8}{\frac{17.1}{\sqrt[]{4}}} \\ t_{H0}=\frac{-12.8}{8.55} \\ t_{H0}=-1.497 \end{gathered}](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20t_%7BH0%7D%3D%5Cfrac%7B75-87.8%7D%7B%5Cfrac%7B17.1%7D%7B%5Csqrt%5B%5D%7B4%7D%7D%7D%20%5C%5C%20t_%7BH0%7D%3D%5Cfrac%7B-12.8%7D%7B8.55%7D%20%5C%5C%20t_%7BH0%7D%3D-1.497%20%5Cend%7Bgathered%7D)
The test statistic under the null hypothesis is -1.497
The p-value is the probability corresponding to the calculated statistic if possible under the null hypothesis.
So you have to calculate the probability of obtaining the value t=-1497
The student t has n-1 degrees of freedom, since the sample taken is n=4, the degree of freedom is 3.
The p-value is then the accumulated probability up to -1.497 under a t-distribution with 3 degrees of freedom:
![p-\text{value}=P(t_3\leq-1497)=0.115653\approx0.1157](https://tex.z-dn.net/?f=p-%5Ctext%7Bvalue%7D%3DP%28t_3%5Cleq-1497%29%3D0.115653%5Capprox0.1157)
The p-value is equal to 0.1157
4)
To make a decision using the p-value, you have to compare the said value with the level of significance, following the decision rule:
- If the p-value ≥ α, do not reject the null hypothesis.
- If the p-value < α, reject the null hypothesis.
The p-value (0.1157) is greater than the significance level (α= 0.05)
The decision is "do not reject the null hypothesis."