Transcript Notes on using the Calculator for Normal Applications

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?
A professor can grade an average of 12 papers per day with a
standard deviation of 1.8 papers. What is the probability that he
can grade between 10 and 13 papers?
The mean time to finish a test is 38 minutes with a standard
deviation of 4.8 minutes. What’s the probability that a person takes
more than 45 minutes to finish the test?
The mean time to run a race is 6.7 minutes with a standard
deviation of 0.37 minutes. Find the probability that it took less
than between 6.5 and 6.8 minutes?
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