Question 1185722
<pre>
On your T-84, assuming first that it's a later model.

Press 2ND VARS 3

Make the screen read

               invNorm
area:0.20
&mu;:45
&sigma;: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</pre>