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Norm Dist: Find Prob


What's the formula to find the z-score? (x-u)/o
what are the steps to finding the probability of a normal distribution? 1. find z score 2. find z score on table
Survey indicates ppl use their cell an average of 1.5 yrs before buying a new one. The stand dev is .25 yrs. Cell phone user randomly selected. Find prob user will use phone for less than 1 yr before buying new on. Assume variable x is normally dist. u=1.5, o=.25, shaded area x<1; z-score=(1-1.5)/.23=-2; P(z<-2)=.0228. So 2.28% of cellular phone users will use their cellular phone for less than 1 yr before buying a new one.
Created by: Erushi Amaya Erushi Amaya