The quality control manager at a computer manufacturing company believes that the mean life of a computer is 120 months, with a variance of 64. If he is correct, what is the probability that the mean of a sample of 89 computers would be less than 118.81 months? Round your answer to four decimal places.

P(X<118.81)=0.0803

Step-by-step explanation:

Assuming the distribution for the mean life is approximately normal, with mean 120 months and variance 64 months^2, we can calculate the parameters for a sampling distribution with sample size = 89 computers.

The sampling distribution mean will be equal to the mean for a single computer:

The standard deviation will be adjusted by the sample size as:

With these parameters, we can calculate the z-score for X=118.81.

Then, the probability that the mean of a sample of 89 computers is less than 118.81 months is:

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for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.