# BUEC 232 Lecture Notes - Lecture 11: Interquartile Range, Probability Plot, Standard Deviation

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Finding the x value for a known probability. Steps to find the x value for a known probability: find the z value for the known probability, convert to x units using the formula: Finding the x value for a known probability: example. Example: let x represent the time it takes (in seconds) to download a video file from the internet. Suppose x distribution is normal with mean 8. 0 and standard deviation 5. 0: now find the x value so that only 20% of all values are below this x (20% of downloads are faster). Finding the x value for a known probability: example: 20% area in the lower tail is consistent with a z value of -0. 84, convert to x units using the formula: Umm what is the interquartile range again: assessing normality, not all continuous random variables are normally distributed, normally distributed data should approximate the mathematically ideal normal distribution.