#### Answer

The mean is 6.5, modes are 4 and 4.5, the median is 4.5, the midrange is 9.5.

#### Work Step by Step

The mean can be counted by summing all the data and dividing it by the number of data: $\frac{6\cdot 4+6\cdot4.5+6+6+8+9+9+13+13+15}{20}=6.5$, the mean is 6.5. The mode is the data occuring the most times, which here are 4 and 4.5 both appearing 6 times. The median is the average of the 1 or 2 (here 2) middle data: (4.5+4.5)/2=4.5, the median is 4.5. The midrange is the average of the highest and the lowest data: (4+15)/2=9.5, the midrange is 9.5. It is common to finish the degree in 4 years but most of the time it takes longer.