The weights of 6-week-old poults (juvenile turkeys) are normally distributed with a mean 8.9 pounds and standard deviation 1.9 pounds. A turkey farmer wants to provide a money-back guarantee that her 6-week poults will weigh at least a certain amount. What weight should she guarantee so that she will have to give her customer's money back only 1% of the time?

A) 4.47 lb
B) 4.02 lb
C) 4.92 lb
D) 3.58 lb

Respuesta :

Answer:

[tex]z=-2.33<\frac{a-8.9}{1.9}[/tex]

And if we solve for a we got

[tex]a=8.9 -2.33*1.9=4.47[/tex]

And the best answer for this case would be:

A) 4.47 lb

Step-by-step explanation:

Let X the random variable that represent the weights of juvenile turkeys, and for this case we know the distribution for X is given by:

[tex]X \sim N(8.9,1.9)[/tex]  

Where [tex]\mu=8.9[/tex] and [tex]\sigma=1.9[/tex]

The z score formula very useful for this case is given by:

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

For this part we want to find a value a, such that we satisfy this condition:

[tex]P(X>a)=0.99[/tex]   (a)

[tex]P(X<a)=0.01[/tex]   (b)

Both conditions are equivalent on this case. We can use the z score again in order to find the value a.  

As we can see on the figure attached the z value that satisfy the condition with 0.01 of the area on the left and 0.99 of the area on the right it's z=-2.33. On this case P(Z<-2.33)=0.01 and P(z>-2.33)=0.99

If we use condition (b) from previous we have this:

[tex]P(X<a)=P(\frac{X-\mu}{\sigma}<\frac{a-\mu}{\sigma})=0.01[/tex]  

[tex]P(z<\frac{a-\mu}{\sigma})=0.01[/tex]

So we have this relation

[tex]z=-2.33<\frac{a-8.9}{1.9}[/tex]

And if we solve for a we got

[tex]a=8.9 -2.33*1.9=4.47[/tex]

And the best answer for this case would be:

A) 4.47 lb