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Normal Distribution Real World Examples Example #1 Maple tree diameters in a forest area are normally distributed with mean 10 inches and standard deviation 2.2 inches. Find the proportion of trees having a diameter greater than 15 inches. Example #2 • White blood cell (WBC) count per cubic millimeter of whole blood has approximately the N(7500, 1750) distribution. The lowest 2% of all WBC counts are defined to be probable risks. How low must one's WBC count be to fall in the at-risk group? Example #3 • The resting heart rate for healthy adult horses averages 46 beats per minute with a standard deviation of 8 beats per minute. A horse whose resting heart rate is in the upper 10% of the distribution of heart rates may have a secondary infection or illness that needs to be treated. How fast must a healthy horse's heart be beating to fall into this at-risk group? Example #4 • When robins’ eggs are weighed, it turns out that they vary according to approximately the normal distribution with mean 17.5 mg and standard deviation 3.5 mg. What proportion of robins’ eggs weigh between 10 mg and 25 mg? How large are the largest 2% of all robins’ eggs? Example #5 The length of human pregnancies from conception to birth varies according to a distribution that is approximately normal with mean 264 days and standard deviation 16 days. What's the probability a pregnancy lasts less that 250 days? What's the probability a pregnancy lasts between 240 and 270 days? Doctors agree that serious thought to labor-inducing procedures ought to accompany any pregnancy that runs in the longest 2% of all pregnancies. At what day should these procedures be considered?