Did you misspell the title ? What does th mean?
Answer:
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:
2-3(x+4)=8
2-3x+12=8
2-3x=-4
-3x=-6
x=2
You would do 8/5 then make it 1 3/5