1. Normal Probabilities
Find the probability P(x ≤ x0), where x is a normally distributed random variable
Click Insert Function (fx)
Select Statistical as your function category
Choose NORM.DIST 1 2

2. Normal Probabilities
You must enter X = The value of the normal distribution for which you would like the cumulative probability P(x ≤ X).
Mean = The mean of the normal distribution.
Standard_dev = The standard deviation of the normal
distribution
Cumulative = True if you want P(x ≤ X).
= False if you want the height of the curve at x. Use
if you would like to graph the
function (not used much in this class).

3. Normal Probabilities
Example: The wind speed at a wind energy farm is approximately normally distributed with a mean of 25 miles per hour and a standard deviation of 7 miles per hour. What percent of the time will the wind speed be below 15 miles per hour?
You must enter X = 15
Mean = 25
Standard_dev = 7
Cumulative = True
So P(x < 15) = .0766

4. Normal Probabilities
Find the X-value giving you probability P(x ≤ X) = P0.
Click Insert Function (fx)
Select Statistical as your function category
Choose NORM.INV 1 2

5. Normal Probabilities
You must enter Probability = The probability P0 for which you would like the value of the standard normal distribution giving you P(x ≤ X) = P0.
Mean = The mean of the normal distribution
Standard _dev = The standard deviation of the normal
distribution

6. Normal Probabilities
Example: An instructor curves the class grades so that the top 10% of the students in class receive an A for the semester. During the past semester, the grades were approximately normally distributed with a mean of 217 points and a standard deviation of 32 points. How many points were needed to earn an A for the semester?
You must enter Probability = .9 Excel wants the probability below the value of X.
You want the value with 10% of the students
above which is the same as 90% of the students below.
Mean = 217
Standard _dev = 32
Your answer is 258