IQ scores are measured with a test designed so that the mean is 99 and the stand

Question

IQ scores are measured with a test designed so that the mean is 99 and the standard deviation is 11. Consider the group of IQ scores that are unusual. What are the Z scores that separate the unusual IQ scores from that are usual? What are the IQ scores that separate the unusual IQ scores from those that are usual? (Consider a value to be unusual if its z score is less than -2 or greater than 2.) What are the z scores that separate the unusual IQ scores from those that are usual? The lower z score boundary is .

Explanation / Answer

An IQ score will be considered unusual if the z- score for it is < -2 or > 2

x = + z *

x1 = 99 + (-2)11 = 77 and x2 = 99 + 2(11) = 121

The cutoff scores are 77 and 121.

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