The mean number of words per minute (WPM) typed by a speed typist is 135 135 with a variance of 100 100 . What is the probability that the sample mean would be greater than 135.7 135.7 WPM if 43 43 speed typists are randomly selected

Answer :

Answer:

[tex] z = \frac{135.7-135}{\frac{10}{\sqrt{43}}}= 0.459[/tex]

And we can find this probability with this way:

[tex] P(z> 0.459) =1 -P(z<0.459)= 1-0.677= 0.323[/tex]

Step-by-step explanation:

For this case w ehave the following info given:

[tex] \mu = 135[/tex] represent the sample mean

[tex] \sigma^2 = 100[/tex] represent the sample variance

[tex] \sigma =\sqrt{100}=10[/tex] represent the deviation

[tex] n = 43[/tex] represent the sample mean selected

For this case we want to find the following probability:

[tex] P(\bar X >135.7)[/tex]

And since the sample size is large enough we can use the following distribution for the sample mean:

[tex]\bar X \sim N(\mu , \frac{\sigma}{\sqrt{n}}) [/tex]

And we can use the z score formula given by:

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

And we can find the z score for the value 135.7 and we got:

[tex] z = \frac{135.7-135}{\frac{10}{\sqrt{43}}}= 0.459[/tex]

And we can find this probability with this way:

[tex] P(z> 0.459) =1 -P(z<0.459)= 1-0.677= 0.323[/tex]

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