Respuesta :
Answer:
a) [tex]P(X<650)=P(\frac{X-\mu}{\sigma}<\frac{650-\mu}{\sigma})=P(Z<\frac{650-625}{70})=P(z<0.357)[/tex]
And we can find this probability with the normal standard table or excel:
[tex]P(z<0.357)=0.639[/tex]
b) [tex]P(X<640)=P(\frac{X-\mu}{\sigma}<\frac{640-\mu}{\sigma})=P(Z<\frac{640-625}{70})=P(z<0.214)[/tex]
And we can find this probability with the normal standard table or excel:
[tex]P(z<0.214)=0.585[/tex]
Step-by-step explanation:
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".
Part a
Let X the random variable that represent the amount of gas of a population, and for this case we know the distribution for X is given by:
[tex]X \sim N(625,70)[/tex]
Where [tex]\mu=625[/tex] and [tex]\sigma=70[/tex]
We are interested on this probability
[tex]P(X<650)[/tex]
And the best way to solve this problem is using the normal standard distribution and the z score given by:
[tex]z=\frac{x-\mu}{\sigma}[/tex]
If we apply this formula to our probability we got this:
[tex]P(X<650)=P(\frac{X-\mu}{\sigma}<\frac{650-\mu}{\sigma})=P(Z<\frac{650-625}{70})=P(z<0.357)[/tex]
And we can find this probability with the normal standard table or excel:
[tex]P(z<0.357)=0.639[/tex]
Part b
[tex]P(X<640)[/tex]
And the best way to solve this problem is using the normal standard distribution and the z score given by:
[tex]z=\frac{x-\mu}{\sigma}[/tex]
If we apply this formula to our probability we got this:
[tex]P(X<640)=P(\frac{X-\mu}{\sigma}<\frac{640-\mu}{\sigma})=P(Z<\frac{640-625}{70})=P(z<0.214)[/tex]
And we can find this probability with the normal standard table or excel:
[tex]P(z<0.214)=0.585[/tex]
