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The Wechsler Adult Intelligence Scale (WAIS) is a common "IQ test" for adults. The distribution of WAIS scores for persons over 16 yrs of age is approximately Normal with mean (100) and Standard Deviation 15,

(a) Whatis the probability that a random chosen individual has a WAIS score of 105 or higher?

(b) What are the mean and standard deviation of the average WAIS score of x for a SRS of 60 people?

(C) What is the Probability that the average WAIS score of an SRS of 60 people is 105 or higher?

Use z-scores and the normal distribution table for these problems.

For example:
a) Use z-score formula: z = (x - mean)/sd

z = (105 - 100)/15 = 0.33

Look at a normal distribution table using z = 0.33 and determine the area under the curve that would represent this z-score and higher (upper tail of the distribution curve). That would then be your probability.

If a sample size is given, that needs to be computed into the formula:
z = (x - mean)/(sd/sqrt of sample size)
Note: sqrt = square root.

I hope this will get you started.

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