TI-83 Instructions

Computing Normal Percentiles

Z is the standard normal random variable.

X is a normal random variable with mean μ and standard deviation σ.

Find c such that P(Z < c) = p.

1. Press 2nd DISTR.  The DISTR menu title is highlighted.
2. Select invNorm, the item #3, or press 3 and skip the next step.
3. Press ENTER.  The phrase invNorm( appears in the display.
4. Enter the value of p.  This number must be between 0 and 1.
5. Press ).
6. Press ENTER.  The value of c appears in the display.

# Find c such that P(Z > c) = p.

1. Compute 1 – p.
2. Use the above procedure to find c such that P(Z < c) = 1 – p.

# Find c such that P(X < c) = p.

1. Press 2nd DISTR.  The DISTR menu title is highlighted.
2. Select invNorm, the item #3, or press 3 and skip the next step.
3. Press ENTER.  The phrase invNorm( appears in the display.
4. Enter the value of p.
5. Press comma.
6. Enter the value of μ.
7. Press comma.
8. Enter the value of σ.
9. Press ).
10. Press ENTER.  The value of c appears in the display.

Find c such that P(X > c) = p.

1. Compute 1 – p.
2. Use the above procedure to find c such that P(X < c) = 1 – p.

# Find za

1. Compute 1 - α.
2. Use the above procedure to find c such that P(X < c) = 1 – α.  This value of c is za.