Introduction

Introduction

Stats Lab 7.2

Central Limit Theorem (Cookie Recipes)

Class Time:

Names:

Student Learning Outcome
  • The student will demonstrate and compare properties of the central limit theorem.

GivenX = length of time (in days) that a cookie recipe lasted at the Olmstead Homestead. (Assume that each of the different recipes makes the same quantity of cookies.)

Recipe # X   Recipe # X   Recipe # X   Recipe # X
1 1   16 2   31 3   46 2
2 5   17 2   32 4   47 2
3 2   18 4   33 5   48 11
4 5   19 6   34 6   49 5
5 6   20 1   35 6   50 5
6 1   21 6   36 1   51 4
7 2   22 5   37 1   52 6
8 6   23 2   38 2   53 5
9 5   24 5   39 1   54 1
10 2   25 1   40 6   55 1
11 5   26 6   41 1   56 2
12 1   27 4   42 6   57 4
13 1   28 1   43 2   58 3
14 3   29 6   44 6   59 6
15 2   30 2   45 2   60 5
Table 7.4

Calculate the following:

  1. μx = _______
  2. σx = _______

Collect the DataUse a random number generator to randomly select four samples of size n = 5 from the given population. Record your samples in Table 7.5. Then, for each sample, calculate the mean to the nearest tenth. Record them in the spaces provided. Record the sample means for the rest of the class.

  1. Complete the following table:
      Sample 1 Sample 2 Sample 3 Sample 4 Sample means from other groups:
               
               
               
               
               
    Means: x¯x¯ = ____ x¯x¯ = ____ x¯x¯ = ____ x¯x¯ = ____  
    Table 7.5
  2. Calculate the following:
    1. x¯x¯ = _______
    2. sx¯x¯ = _______
  3. Again, use a random number generator to randomly select four samples from the population. This time, make the samples of size n = 10. Record the samples in Table 7.6. As before, for each sample, calculate the mean to the nearest tenth. Record them in the spaces provided. Record the sample means for the rest of the class.
      Sample 1 Sample 2 Sample 3 Sample 4 Sample means from other groups
               
               
               
               
               
               
               
               
               
               
    Means: x¯x¯ = ____ x¯x¯ = ____ x¯x¯ = ____ x¯x¯ = ____  
    Table 7.6
  4. Calculate the following:
    1. x¯x¯ = ______
    2. sx¯x¯ = ______
  5. For the original population, construct a histogram. Make intervals with a bar width of one day. Sketch the graph using a ruler and pencil. Scale the axes.

     
    This is a blank graph template. The horizontal axis is labeled Time (days) and the vertical axis is labeled Frequency.
    Figure 7.13
  6. Draw a smooth curve through the tops of the bars of the histogram. Use one to two complete sentences to describe the general shape of the curve.
Repeat the procedure for n = 5.
  1. For the sample of n = 5 days averaged together, construct a histogram of the averages (your means together with the means of the other groups). Make intervals with bar widths of 1212 day. Sketch the graph using a ruler and pencil. Scale the axes.
    This is a blank graph template. The horizontal axis is labeled Time (days) and the vertical axis is labeled Frequency.
    Figure 7.14
  2. Draw a smooth curve through the tops of the bars of the histogram. Use one to two complete sentences to describe the general shape of the curve.
Repeat the procedure for n = 10
  1. For the sample of n = 10 days averaged together, construct a histogram of the averages (your means together with the means of the other groups). Make intervals with bar widths of 1212 day. Sketch the graph using a ruler and pencil. Scale the axes.
    This is a blank graph template. The horizontal axis is labeled Time (days) and the vertical axis is labeled Frequency.
    Figure 7.15
  2. Draw a smooth curve through the tops of the bars of the histogram. Use one to two complete sentences to describe the general shape of the curve.
Discussion Questions
  1. Compare the three histograms you have made, the one for the population and the two for the sample means. In three to five sentences, describe the similarities and differences.
  2. State the theoretical (according to the clt) distributions for the sample means.
    1. n = 5: x¯x¯ ~ _____(_____, _____)
    2. n = 10: x¯x¯ ~ _____(_____, _____)
  3. Are the sample means for n = 5 and n = 10 close to the theoretical mean, μx? Explain why or why not.
  4. Which of the two distributions of sample means has the smaller standard deviation? Why?
  5. As n changed, why did the shape of the distribution of the data change? Use one to two complete sentences to explain what happened.