A statistician wishes to determine the difference between two population means. A sample of 18 items from Population #1 yields a mean of 205 with a standard deviation of 12. The sample of 15 items from Population #2 yields a mean of 190 with a standard deviation of 10. Assume that the values are normally distributed in each population.   How many degrees of freedom are there for this test? a. 18 b. 14 c.15 d. 17

Features Features Normal distribution is characterized by two parameters, mean (µ) and standard deviation (σ). When graphed, the mean represents the center of the bell curve and the graph is perfectly symmetric about the center. The mean, median, and mode are all equal for a normal distribution. The standard deviation measures the data's spread from the center. The higher the standard deviation, the more the data is spread out and the flatter the bell curve looks. Variance is another commonly used measure of the spread of the distribution and is equal to the square of the standard deviation.