1.If we know z-values we can back-calculate to get the original x-value or data point.Assume that the mean of a data set is 15 and the standard deviation is 3.We have a probability (area or percentage of data points) to the LEFT of this +z-value equal to 0.9015What is this z-value (the standardized standard deviation)?

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Using that z-value what is the original x-value that when standardized became that z-value?

z = (x - mean) / SDsolve for x since you know the other 3 values (basic algebra).