An adjusted histogram is the conversion of a frequency distribution to a probability distribution.

The probability that a continuous random variable assumes some value in an interval is represented by the area under the portion of the continuous curve of that interval.

A uniform distribution has the same frequency for each value of x.

The standard normal random variable is a normal variable with mean = 0 and standard deviation = 1. Its value is represented by the symbol, z.

   (the data value minus the mean divided by the standard deviation)
 

The z-score or z values of a normal variable, x corresponds to the number of standard deviations of about the mean

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Central Limit Theorem: As samples size, n increases the sample distribution approaches the normal distribution.  (n )