A production process is checked periodically by a quality control inspector. The inspector selects simple random samples of 30 finished products and computes the sample mean product weights x¯. If test results over a long period of time show that 5% of x¯ the values are over 2.1 pounds and 5% are under 1.9 pounds, what are the mean and the standard deviation for the population of products produced with this process?

Respuesta :

Answer:

μ = 2.0

σ = 0.3330

Step-by-step explanation:

see solution below

Ver imagen micahdavid126

The mean and the standard deviation for the population of products produced with the process are 2.0 and 0.3329

Start by calculating the population mean using:

[tex]\mu = \frac{L + U}{2}[/tex]

Where:

L = 1.9 and U = 2.1

So, we have:

[tex]\mu = \frac{1.9 + 2.1}{2}[/tex]

[tex]\mu = 2.0[/tex]

The z value when p = 5%, from z table of probability is:

z = -1.645

Also, we have the z-score to be:

[tex]z = \frac{x - \mu}{\sigma/\sqrt n}[/tex]

So, we have:

[tex]-1.645 = \frac{1.9 - 2.0}{\sigma/\sqrt {30}}[/tex]

[tex]-1.645 = \frac{-0.1}{\sigma/\sqrt {30}}[/tex]

[tex]16.45 = \frac{1}{\sigma/\sqrt {30}}[/tex]

Cross multiply

[tex]\sigma/\sqrt {30} * 16.45 = 1[/tex]

Take the square root of 30

[tex]\sigma/5.477* 16.45 = 1[/tex]

[tex]\sigma = 0.3329[/tex]

Hence, the mean and the standard deviation for the population of products produced with the process are 2.0 and 0.3329

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