I am having trouble this week with the normal versus standard normal density curves. For example in one problem I have a mean of 5, a standard deviation of 4 and need to shade in a region that represents the probability of obtaining a value from the distribution that is less than 9. To begin I need to get the z-score by subtracting the mean of 5 from the probability of 9, then dividing the sum by the standard deviation of 4. Solving this equation I get a z-score of 1.

With a z-score of 1 and needing to obtain a value less than 9, I must now shade in the appropriate region of the chart, and this is where my problem lies. I cannot figure out how the area to be shaded is determined. I know I need to shade the region either to the left or right of 1, but I don’t know how far to shade or why I shade one side over the other. 

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