Suppose that replacement times for washing machines are normally distributed with a mean of 9.3 years and a standard deviation o
f 1.1 years. find the probability that 70 randomly selected washing machines will have a mean replacement time less than 9.1 years. write your answer as a decimal rounded to 4 places.
The probability will be found as follows: z-score is given by: z=(x-μ)/σ where: mean-μ=9.3 standard deviation-σ=1.1 but σ/√n=1.1/√70=0.1315 thus the z-score will be: z=(9.1-9.3)/0.1315 z=-1.5209 thus: P(x<9.1)=P(z<-1.5209)=0.0643
