The z-score table is the cumulative distribution for the Standard Normal Distribution. In real life very many random variables can be modelled, at least approximately, by the Normal (or Gaussian) distribution. It will have its own mean and variance but the Z transform converts it into a standard Normal distribution (mean = 0, variance = 1). The Z-distribution is then used to make statistical inferences about the data.
However, there is no simple analytical method to calculate the values of the distribution function. So, it has been done and tabulated for easy reference.
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If the sample size is less then 30 use the T table, if greater then 30 use the Z table.
(527-500)/100= Z-score. Then, you should look at the table for this given Z score
z score = (test score - mean score)/SD z score = (87-81.1)/11.06z score = 5.9/11.06z score = .533You can use a z-score chart to calculate the probability from there.
A z-score of 0 means the value is the mean.
The z-score must be 1.87: the probability cannot have that value!