Calculating a value for the value of P( x < )

1. Finding x:

The TI-83/84 is equiped with a built in function called invNorm (p, , ). It computes where p = P(x < ) which is the area under the standard normal curve between to the left of . This is also the x-value for the pth percentile.

To calculate x for a p = 0.9, =500 and = 100, that is the area under the normal curve is 0.9 and this area is to the left of some x value, press 2nd VARS [DISTR], ARROW DOWN to select 3:invNormal(, and then press ENTER.

After area: type . 9 ENTER, after : type 500 ENTER and after : type 100 ENTER, and then press ENTER again. See the results below.

Thus 90% of the x values lie below x = 628.2.