Problems with normal probabilities

The position of the graphically represented keys can be found by moving your mouse on top of the graphic.
The row of round buttons at the top do not count as a row. Row 1 starts with .

 Computing probabilities The problem is finding P(X b) where X is a random variance with a specified mean and standard deviation. Normalize the X variable by subtracting the mean, then dividing by the standard deviation: Enter X, press , enter the mean and press . Press , enter the standard deviation and press . Press (you should see DISTR in blue brackets above the key). You'll see three choices on the screen, press ( R( ).

Worked Out Examples

In the following examples, we list the exact key sequence used to find the answer.  We will list the keys by the main symbol on the key.  In parentheses, we will list a helpful mnemonic, e.g. we will list ex as (ex).

 Question 1: Let X be a random variable with m=50 and s=4. Compute P(X < 51). Solution: (DISTR) ( P( ) . You should get 0.59871 as the first five decimal places. Question 2: Let X be a random variable with m=10 and s=8. Compute P(X >12). Solution:  (DISTR) (R( ) . You should get 0.40129 as the first five decimal places. Question 3: Let X be a random variable with m=100 and s=12. P(100 < X < 103). Solution:  (DISTR) ( Q( ) . You should get 0.09871 as the first five decimal places. Notice that P will always be 50 more than Q. Also notice that P and R will add up to one.

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