Statistics: Mean and Standard Deviation?

Let the variable continuous variable X represent IQ scores of 12 year olds. X is Normal with a mean of 100 and a standard deviation of 16.





a. ______________Jessica is a 12-yar old and has an IQ of 132. What proportion of 12-year-olds have IQ scores less than Jessica’s?




















b. ______________Mike is 20 years old and has an IQ of 144. 20-yr-olds have IQs that are normal with mean 120 and standard deviation 20. Standard scores (z) allow direct comparison of scores from different normal distributions. Relative to their respective age groups, who has a higher IQ, Jessica or Mike?























c. _______________What proportion of 12-year-olds have IQ scores below 84?























d. ________________ What proportion of 12-year-olds has IQ scores between 84 and 116?


e. _____________ What IQ score is needed to be in the top 10% of the distribution (90th percentile) of 20-year-olds?

Statistics: Mean and Standard Deviation?
a) - 97.7%


b) - Jessica


c) 15.9%


d) 68.2%


e) 149.6
Reply:You need to do your own homework. I suggest you look in your book for the information about the Empirical Rule. Follow the examples in the book and you should be able to determine these answers.