Lesson 4
1. Lesson 4
1.4. Explore 3
Module 4: Statistical Reasoning
The statistics function for normal distributions on a calculator can also be used to determine the percent of data that is less than a specific data value. To access the statistical function for normal distribution on your calculator, you may press 
and then select “2: normalcdf(.”
You will now enter four values separated by commas. The first value that is entered is the lower bound. This is the value that would be on the furthest left-hand side of the curve. In the example of the muffler, the least amount of time a muffler could last is zero years. The next value is the upper bound, or 6.5 years. Finally, the mean and standard deviation are entered. So, the area under the normal distribution that is less than a value of 6.5 years is 0.348 647 533 9 or 34.9%.
When calculating the area under a curve, you may find that you get slightly different results depending on whether you use the z-score table or the statistics function for normal distribution on your calculator. The z-score table uses a rounded z-score for identifying the fraction of data that is to the left of a particular z-score.