Question

mean absolute deviation of 75, 89, 145, 85, 80, 92, 104, 90, 100?

Answer 1

First, compute the mean: $m=\frac{75+89+145+85+80+92+104+90+100}9=\frac{860}9=95.555$

Next compute the absolute deviations for each datapoint:
|75-95.555|=20.555
|89-95.555|=6.555
|145-95.555|=49.445
|85-95.555|=10.555
|80-95.555|=15.555
|92-95.555|=3.555
|104-95.555|=8.445
|90-95.555|=5.555
|100-95.555|=4.445

Next we'll take the mean of these deviations: $\frac{20.555+6.555+49.445+10.555+15.555+3.555+8.445+5.555+4.445}9=\frac{124.665}9=13.8517$

The mean absolute deviation of your data is 13.8517