SOLUTION: Let's say you have scores on a IQ test that form a normal distribution with a mean of 100 and a standard deviation of 15. What is the probability of selecting an individual from t

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Question 388341: Let's say you have scores on a IQ test that form a normal distribution with a mean of 100 and a standard deviation of 15. What is the probability of selecting an individual from this population with a score above 120.
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Step 1) First find the corresponding z-score


z=%28x-mu%29%2Fsigma=%28120-100%29%2F15=20%2F15=1.333


Step 2) Now find the probability P(X > 120) by finding P(Z > 1.333). Since the two are equivalent, this is possible.


Either use a table or a calculator to find this probability. I used a TI 83 and entered "normalcdf(1.333,1000)" and got the approximate value 0.09121


Note: you can find "normalcdf" by hitting "2nd" then "vars". Once you find the function, you just need to


So P(Z > 1.333) = 0.09121, which means that the probability is 0.09121 (ie about a 9.121% chance)