CK-12-Basic Probability and Statistics Concepts - A Full Course

6.5. Empirical Rule http://www.ck12.org

20 15 21 24 7 19 10 17 15 22 31 19 20 21

21 9 12 26 24 28 19 16 24 11 17 31 25 13

16 18 22 32 9 15 19 27 14 25 32 29

Answer:

You can use the data from the 1-Var Stats calculation to draw the normal distribution curve:

According to the data, the mean of the times is approximately 19.9 minutes, and the standard deviation is approxi-
mately 6.6 minutes. Therefore, the normal distribution curve can be drawn as follows:

Since 2.35%+ 0 .15%= 2 .5% of the times are below 6.7 minutes, a student must complete a Sudoku puzzle in 6.7
minutes to be in the top 2.5%.

Practice

1. What percentage of the data in a normal distribution is between 1 standard deviation below the mean and 2
   standard deviations above the mean?


2. What percentage of the data in a normal distribution is between 3 standard deviations below the mean and 1
   standard deviation above the mean?


3. What percentage of the data in a normal distribution is more than 2 standard deviations above the mean?