Historically, these bolts have an average thickness of 10.1 mm. A recent random sample of 10 bolts yielded these thicknesses:

9.7 9.9 10.3 10.1 10.5 9.4 9.9 10.1 9.7 10.3

a. Find the sample mean and standard deviation for these data.
b. Assume that the historical average is true. Calculate the observed value of the t-statistic.
c. What is the probability of these statistics (or worse) if the true mean were 10.1 mm?

Respuesta :

Answer:

a) Sample mean = 9.99

Sample standard deviation = 0.3348

b) -1.0389

c) 0.1631

Step-by-step explanation:

We are given the following in the question:

9.7, 9.9, 10.3, 10.1, 10.5, 9.4, 9.9, 10.1, 9.7, 10.3

a) sample mean and standard deviation

Formula:

[tex]\text{Standard Deviation} = \sqrt{\displaystyle\frac{\sum (x_i -\bar{x})^2}{n-1}}[/tex]  

where [tex]x_i[/tex] are data points, [tex]\bar{x}[/tex] is the mean and n is the number of observations.  

[tex]Mean = \displaystyle\frac{\text{Sum of all observations}}{\text{Total number of observation}}[/tex]

[tex]Mean =\displaystyle\frac{99.9}{10} = 9.99[/tex]

Sum of squares of differences = 1.009

[tex]S.D = \sqrt{\dfrac{1.009}{9}} = 0.3348[/tex]

b) observed value of the t-statistic

Formula:

[tex]t_{stat} = \displaystyle\frac{\bar{x} - \mu}{\frac{\sigma}{\sqrt{n}} }[/tex]

Putting all the values, we have

[tex]t_{stat} = \displaystyle\frac{9.99 - 10.1}{\frac{0.3348}{\sqrt{10}} } = -1.0389[/tex]

c) probability of these statistics (or worse) if the true mean were 10.1 mm

Degree of freedom =  n - 1 = 9

Calculating the value from the table

[tex]P(x < 9.99) = 0.1631[/tex]

0.1631 is the the probability of these statistics (or worse) if the true mean were 10.1 mm