SOLUTION: Let us assume that the grades of 500 students are normally distributed with 𝜇=45 and standard deviation 𝜎=20. If the 20% of the students get excellent, what is the grade that

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Question 1185722: Let us assume that the grades of 500 students are normally distributed with 𝜇=45 and standard deviation 𝜎=20. If the 20% of the students get excellent, what is the grade that determines the excellent? (What is 𝛸 value?)
Answer by Edwin McCravy(20060)   (Show Source): You can put this solution on YOUR website!
On your T-84, assuming first that it's a later model.

Press 2ND VARS 3

Make the screen read

               invNorm
area:0.20
μ:45
σ:20
Tail: LEFT CENTER RIGHT
Paste

Use the down arrow key to scroll to highlight RIGHT, 
press ENTER to highlight. Then scroll to Paste and press 
ENTER again.

You'll see this:

invNorm(0.20,45,20,RIGHT)

Press ENTER

Read 61.83242467           <-- X value

Round the way you were told.

If your calculator is too old to have "LEFT CENTER RIGHT", 
then it reads only left, so you'll have to make it read:

invNorm(1-0.20,45,20) then press ENTER.

Edwin
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