### Home > CCA2 > Chapter 9 > Lesson 9.3.3 > Problem 9-104

Do you remember the students tardy to Ms. Greene’s class? Now that you have investigated how to create and use a normal distribution, model the number of tardy students Ms. Greene actually recorded using a normal distribution. The data Mrs. Greene gathered for 30 days is shown in the table below. Homework Help ✎

Number of tardy students per day

2

1

2

3

54

3

3

0

33

3

1

2

33

4

2

3

34

3

3

2

42

2

3

5

1*checksum 82*On your calculator, recreate the relative frequency histogram for the number of tardy students that is shown in problem

Find the mean and standard deviation of the number of tardy students.

On your calculator, model the data with a normal distribution by pressing

and entering [DISTR] normalpdf(X, *mean*,*standard deviation*). Sketch the model with the histogram.According to your model, on what percentage of days were 4 people tardy? Shade this proportion on a new sketch of the model, and calculate the proportion using normalcdf(

*lower*,*upper*,*mean*,*standard deviation*) on your calculator.Assume that the last 30 days in Mrs. Greene’s class were representative of the 180 days in the whole school year. According to your model, how many days this year can Mrs. Greene expect 4 or more tardy students? Sketch the area representing these days on a new graph of the model.

You will need to use your calculator to complete this problem.

Click here for TI-83+/TI-84+ calculator instructions.

≈ 11%

Be sure to sketch and shade the model.

normalcdf(4, 10^99, 2.7333, 1.1427)