what is the mean absolute deviation (mad) of the data set?

{21.5, 26.6, 25.8, 23.1, 20.1, 32.9}

round to the nearest tenth, if necessary

First you find the mean of your data set-add all of the numbers and divide by how many numbers you have.=25

Then you find the difference of your mean and each of the numbers in the data set.(subtract each number from the mean and write that number down)
25-21.5=3.5, 26.6-25=1.6, 25.8-25=.8, 25-23.1=1.9, 25-20.1=4.9, 32.9-25=7.9
Finally, find the mean of the new numbers you got when you subtracted each number from the mean.
3.5+1.6+.8+1.9+4.9+7.9=20.6/6=3.43 MAD

This mean you found is called the MAD or Mean Absolute Deviation. Hope his helps.