Lesson 3
1. Lesson 3
1.5. Explore 3
Module 4: Statistical Reasoning
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Normal curves are a useful tool for quality control departments as well. For instance, the normal distribution might provide an accurate model for the distribution of masses of chocolate bars produced at a factory or the lifespan of a product.
Read “Example 4: Analyzing data to solve a problem” on pages 276 and 277 of your textbook. Consider why it is important that Shirley first determine whether the data approximates a normal distribution.
To create a normal curve on top of the histogram, draw midpoints at the tops of the bars and then connect them with a smooth curve.
To create a normal curve on top of a histogram on your graphing calculator, go into STAT PLOT and turn on “Plot2.” Set the type to be a connected line graph, and use the same lists as you used for your histogram. When you press GRAPH, a frequency polygon will be displayed. If your histogram approximates a normal distribution, then your curved line will approximate a normal curve. 
When attempting problems with normally distributed data, sketching the normal distribution is a very useful way to help you visualize the problem. Make sure to write down the data values on the diagram for one, two, and three standard deviations above and below the mean.
Self-Check 2
- Complete “Practising” questions 4, 8, 10, and 11 on pages 279 to 281 of your textbook. Answer
- Complete “Closing” question 15 on page 281 of your textbook. Answer