Answer:
Yes. At this significance level, there is evidence to support the claim that there is a difference in the ability of the brands to absorb water.
Step-by-step explanation:
<em>The question is incomplete:</em>
<em>The significance level is 0.05.</em>
<em>The data is:</em>
<em>Brand X: 91, 100, 88, 89</em>
<em>Brand Y: 99, 96, 94, 99</em>
<em>Brand Z: 83, 88, 89, 76</em>
We have to check if there is a significant difference between the absorbency rating of each brand.
Null hypothesis: all means are equal
![H_0:\mu_x=\mu_y=\mu_z](https://tex.z-dn.net/?f=H_0%3A%5Cmu_x%3D%5Cmu_y%3D%5Cmu_z)
Alternative hypothesis: the means are not equal
![H_a: \mu_x\neq\mu_y\neq\mu_z](https://tex.z-dn.net/?f=H_a%3A%20%5Cmu_x%5Cneq%5Cmu_y%5Cneq%5Cmu_z)
We have to apply a one-way ANOVA
We start by calculating the standard deviation for each brand:
![s_x^2=30,\,\,s_y^2=6,\,\,s_z^2=35.33](https://tex.z-dn.net/?f=s_x%5E2%3D30%2C%5C%2C%5C%2Cs_y%5E2%3D6%2C%5C%2C%5C%2Cs_z%5E2%3D35.33)
Then, we calculate the mean standard error (MSE):
![MSE=(\sum s_i^2)/a=(30+6+35.33)/3=71.33/3=23.78](https://tex.z-dn.net/?f=MSE%3D%28%5Csum%20s_i%5E2%29%2Fa%3D%2830%2B6%2B35.33%29%2F3%3D71.33%2F3%3D23.78)
Now, we calculate the mean square between (MSB), but we previously have to know the sample means and the mean of the sample means:
![M_x=92,\,\,M_y=97,\,\,M_z=84\\\\M=(92+97+84)/3=91](https://tex.z-dn.net/?f=M_x%3D92%2C%5C%2C%5C%2CM_y%3D97%2C%5C%2C%5C%2CM_z%3D84%5C%5C%5C%5CM%3D%2892%2B97%2B84%29%2F3%3D91)
The MSB is then:
![s^2=\dfrac{\sum(M_i-M)^2}{N-1}\\\\\\s^2=\dfrac{(92-91)^2+(97-91)^2+(84-91)^2}{3-1}\\\\\\s^2=\dfrac{1+36+49}{2}=\dfrac{86}{2}=43\\\\\\\\MSB=ns^2=4*43=172](https://tex.z-dn.net/?f=s%5E2%3D%5Cdfrac%7B%5Csum%28M_i-M%29%5E2%7D%7BN-1%7D%5C%5C%5C%5C%5C%5Cs%5E2%3D%5Cdfrac%7B%2892-91%29%5E2%2B%2897-91%29%5E2%2B%2884-91%29%5E2%7D%7B3-1%7D%5C%5C%5C%5C%5C%5Cs%5E2%3D%5Cdfrac%7B1%2B36%2B49%7D%7B2%7D%3D%5Cdfrac%7B86%7D%7B2%7D%3D43%5C%5C%5C%5C%5C%5C%5C%5CMSB%3Dns%5E2%3D4%2A43%3D172)
Now we calculate the F statistic as:
![F=MSB/MSE=172/23.78=7.23](https://tex.z-dn.net/?f=F%3DMSB%2FMSE%3D172%2F23.78%3D7.23)
The degrees of freedom of the numerator are:
![dfn=a-1=3-1=2](https://tex.z-dn.net/?f=dfn%3Da-1%3D3-1%3D2)
The degrees of freedom of the denominator are:
![dfd=N-a=3*4-3=12-3=9](https://tex.z-dn.net/?f=dfd%3DN-a%3D3%2A4-3%3D12-3%3D9)
The P-value of F=7.23, dfn=2 and dfd=9 is:
![P-value=P(F>7.23)=0.01342](https://tex.z-dn.net/?f=P-value%3DP%28F%3E7.23%29%3D0.01342)
As the P-value (0.013) is smaller than the significance level (0.05), the null hypothesis is rejected.
There is evidence to support the claim that there is a difference in the ability of the brands to absorb water.