Assume that adults have an IQ scores that are normally distributed with a mean of u=105 and a standard deviation of 20. Find the probability that a randomly selected adult has an IQ less than 125.

Answer 1

You can answer this question with a TI-84, Excel or Google spreadsheet, or with a table. I will walk you through how to solve this with a TI-84.

Since this is a Normal Cumulative Distribution Function, you will press the following keys:

"2nd", "DISTR", (scroll down and select option two) "2:normalcdf("

You should see "normalcdf(" pasted to your home screen. Next you need to tell it the lower bound, upper bound, mean, and standard deviation, separated by commas. Your screen will look like this: "normalcdf(0, 125, 105, 20)".

When you press enter, it will give you the value of .8413... this is the chance. You can multiply it by 100 to obtain the percent.

For a more detailed explanation, help using Excel or a table, feel free to contact me and we'll schedule a lesson.