Using the Calculator for Normal Distributions

Standard Normal

Go to 2nd Distribution Find #2 – Normalcdf

Key stroke is Normalcdf(Begin, end)

If standardized, then mean & st. deviation do not have to be given.

Find P(1.1<z<1.89)

Press: Normalcdf (1.1, 1.89) enter

You should get 0.1063

Check By chart method:

0.9706 – 0.8643 = 0.1063

To represent infinity we use

1E99 (1X10^99) for positive infinity

-1E99 (-1x10^99) for negative infinity

Represent in notation with ∞

Find: P(z<2.07)

Find: P(z>0.12)

Try the following

P(z < -1.23)

P(-1.2<z<2.05)

P(z>1.23)

Average age of a student is 20 with standard deviation of 2.1 years. What’s the probability that a student’s age is more than 23?

Finding a percentile….

Use Invnorm(%) to get the z-score

The mean score on a test is 70 with = 3. What’s the cutoff score for the 90th percentile?

If the mean test score is 88 with standard deviation of 2, find the cutoff scores for the middle 40%.

So if the mean is 34 and you know that 78% scored less than 36, what’s the standard deviation?

If 28% scored less than 36 on a test, and 87% scored more than 34, what’s the mean and the standard deviation?

Homework

Worksheet